Citroen XM Forum

I de-rusted the rest of the tailgate outer spots and notices some at the bottom edge, internally, under the latch unit where there is a strengthening plate welded on.
I think water has been entering via the latch handle area and running down inside the skin. The construction is such that any water that does enter via the light units, or latch unit drains out of the bottom of the tailgate, however under the latch area is only primed, no top coated and is made of more than one sheet of steel, so has edges, where paint won't cover well.

I tried scraping and wire brushing this area, but access is extremely limited, with no chance of being able to de-rust completely, so have resorted to using a phosphate rust converter, which converts and encapsulates rust to make it stable and impervious to oxygen.

I have given this and whilst I had it available, also the outer bare patches, three coats of converter.

At the sides of the tailgate I had noticed one patch each side where the seam sealer had worn away, so I squeezed in some new and then painted all bare areas with two coats of brush painted primer. I'm not bothered about appearance as these are all discrete areas, behind external trims/light units. Brushing means no masking, and a thicker paint coat.
In the internal latch area I also added a single spray coat of primer, to reach any awkward areas the brush couldn't reach.

Time to mix black and blue paint at a 73% black ratio. I made up a total of 68 grammes, (50+28)which was sufficient for two coats.
I chose to use Hamemrite as it is a quick drying and hard paint, so I can rebuild the tailgate quickly and the paint should provide reasonable wear protection.
The machine enamel I have would give a better brush painted finish, but is slower to dry and will take longer before it becomes as hard-wearing.


I painted all touch points, including the ones on the body coloured plastic bar that had rubbed through the original tailgate paint.


I Also painted over where the seam sealer has been replaced as well as some areas where the original paint was still sound, as I want to add additional protection.
I painted the underside of the tailgate as the interior plastic trim had rubbed through the paint.


I recovered the boot tie downs from their acid bath and gave them a final scrub. These were originally very rusty.


While I had, clean, left over acid I scrubbed the rubber glass trim, which was encrusted with so-far, impossible to remove lichen. Not quite gone in sixty seconds, but pretty good.
You can also see in the below image the fresh paint around the spoiler mounting holes. The paint is a good colour match, but isn't metallic, but it doesn't matter as it is under the spoiler foot.

I remounted the external fittings onto the tailgate and wanted to ensure no water could enter.
The tailgate metalwork has an extra internal layer behind the lower lights, that is designed such that any water entering will be directed to the base and out of the drain holes and judging from the rusty screws inside the tailgate and water found in the boot, water has been entering. On opening the tailgate any water left in this layer will run inside the boot inner trim panel and then into the boot.

As well as fitting new rubber spoiler seals, I have used non-setting Butyl mastic on all areas I think may have leaked. The spoiler seals are an obvious place, but I also think the painted plastic trim fixing screws have been leaking water in.
Additionally, water runs behind the upper light-bar, down the tailgate and inside via the latch handle area, which doesn't have the additional funnelling metalwork.

Spoiler seals, including mastic.

The latch handle sits in a large A shaped hole with a rubber seal. To ensure the seal doesn't leak internally I added mastic into the rebate, before fitting it into the hole. It clips round the metalwork, so when water enters this seal at the top, it can migrate from the outside to the inside as it runs down the vertical section.

The latch handle simply abuts the rubber seal, but is covered by a plastic hood, which is part of the painted trim panel.

Normally one fits the painted trim after the lights and light bar, but I wanted to add mastic so fitted it first.

Mastic round the screw holes and the A shape that should tightly press on the rubber seal face. I was concerned there is insufficient pressure to create a reliable seal.

I added additional mastic once the panel was installed. I believe this is where water was leaking in and really want to keep any water on the outside of the panel.

Refitting the tailgate lights meant undoing the painted trim panel screws, apart from the ones round the latch unit, to allow the trim to be flexed out, allowing the lights to pass underneath.
Tip: If painting the inside of the tailgate use a light colour/white. I painted it in dark blue body colour and it made it difficult to see the screw holes for the painted trim panel.

When refitting the latch unit and light units I greased all moving parts and electrical connectors.

I'll monitor the boot for water intrusion before refitting the linings, however judging by the rust on the inner tailgate metalwork, by the boot latch, do think the water ingress has been these areas.
As an aside, I've always been aware this car has suffered with a lot of tailgate glass internal condensation, which I now think is due to this water leaking in.
I always thought it was due to the sunroof, but maybe not all is.

Having left the boot linings out for a few weeks, with pieces of cardboard on the floor, to see if any water entered the boot. Finding it stayed completely dry I started installing them.

On went the tailgate interior panel
I primed and painted the luggage restraining rings
Painted and re-installed the vent mesh which was suffering from broken retaining tabs. I used stainless lock wire to re-attach them to the liner.
Re-installed the boot carpet, side liners and luggage tie-down rings, connected the boot lamp switch carefully routing the wires down so they don't become chapped and chafed, then fitted the protector plate.

The carpet you see in these images is a second carpet I use as a protector, the proper carpet and soundproofing are fitted underneath.


In went the parcel shelf and lastly the rear protector plate screw caps.

It's beginning to look like a compete car again.

Looks great, great restorer!!

Due to the tailgate rubber seal having a few signs of deterioration I installed another one, which was even more contracted, so had a larger gap.
To fill the gap I cut a length off the old seal and inserted it in, attempting to bond it in with solvent adhesive, which was partially successful as the two profiles of rubber are slightly different, with the older seal having larger ones.

I also fitted a replacement tailgate bump stop as the left one was broken since before my ownership.

I tested the lights and when pressing the brake pedal received error messages for both left and right stop lamps having failed.
The brake lamps were both illuminating as seen in a previous image.


As both lamps were being reported to have failed simultaneously I decided to check the secondary Gnd leads, so removed the boot latch protector, seal and liners to check.


All seemed fine so I wondered if the bulb failure module was faulty, but thought I would check the lamp holders for corrosion. I unclipped the holders and bulbs, sprayed the holders and bulb contacts with contact cleaner, wiped and re-installed the bulbs.

Once again I checked the lamps were illuminating.


I had noted the cloudy bulbs but thought they were tail-lights, so not relevant.

I checked the bulbs to see what they were, finding the indicator lamp to be P21w as expected, the brake lamp to be a stop/tail lamp (21/5W).
I was surprised when the lower bulbs were P21w, thinking that was too bright for tail-lights.
Then the penny dropped...
The centre bulbs are stop/tail lights, the lower bulbs are stop lights only. The secondary tail-light is mounted on the tailgate so there are two tail-lights and two stop lamps, each side of the car.
It's easy to be sucked down a Rabbit hole when working on a fault. Check everything and don't overthink issues...KISS

These bulbs appear to be the originals, so I found a couple more and replaced them.


I also tested with the hazard lights on to check those as well.


At the front of the car two of the brake pipe support clips had broken rivets, so I drilled them and installed self tapping screws to hold them on.

Degens wrote: Thu Sep 24, 2026 5:21 pm Looks great, great restorer!!

Thanks Hans.
After fifteen years of ownership having rescued it after seven years off the road, of which over six were it resting in a field, having to re-register it due to being declared scrapped, then the last ten years using it as my daily use car, it having an oil leak which I needed to deal with, the rest is just a bit of maintenance to make it last longer. Rust is the killer of an XM, so I like to keep on top of it. I rustproofed the box sections of this car some years ago, so they are sound.

This image taken yesterday shows the drivetrain is completely leak free, which is no small feat for an XUD engine.

After washing the car I checked the tailgate for any water intrusion and on removing the lights access panels saw there was.

Having already sealed the painted plastic bar fittings I looked closely at the light units and saw water had entered via the upper section of the seal, run down the lamp units and instead of being captured by the built in metal scoop and deflected into the bottom of the tailgate, had dripped into the plastic liner.

I'm now sure this is how water enters the boot interior, wets the carpet and linings and causes rust, as the plastic liner is mounted inside the tailgate seal, so the only way water can then exit is into the boot.


I am keen to keep water out of the car and tailgate, so investigated.


I could see the rubber seal a the top of the lamp unit was only just being trapped by the metalwork, the majority of the seal was not compressed. Over 34 years this has compressed the seal edge and now allows water to pass through.

To remove the lamp unit one has to unscrew the painted plastic bar then the lamp units unbolt.

The seal is clearly compressed along the upper edge, with evidence of water intrusion.


I tried reinstalling the lamp units higher, but the alignment tabs on the top side stop it being mounted high enough for the seal to be fully covered by the metalwork.

As a result of the seal being only compressed along it's top edge it has distorted downwards, so I cut some thin plastic strips and installed them inside the seal to push it upwards a little.


Even with the seal being restrained upwards it was still only contacting the metalwork along it's upper edge, so I resorted to adding some non-setting butyl mastic along the top edge only, before installing the lamp units.


When fitting the lamp units place them in as high as possible and tighten fastenings loosely, then pull the unit down just enough to be able to fit the painted plastic bar, lastly push the lamp units upwards against the plastic bar and tighten the retaining nuts fully.

After testing using a squirty bottle and water I am now confident no more water will enter the tailgate through these lamp units.

Having noticed rust inside another XM tailgate recently I then checked my sable car and found the same issue was happening, but no rust as yet.

Sable car tailgate lamp upper rubber seal not covered by metalwork and allowing water to pass into the tailgate.


It appears the stamping of the metal has allowed too much tolerance at the upper edge, so the seals are not being compressed sufficiently to stop water ingress. This is a design stage issue, not a manufacturing one: it's difficult to resolve properly without adding more metal to the tailgate skin, so it covers the rubber seal fully.
It appears as though the metal aperture in the tailgate skin was set in relation to the solid plastic of the top of the lamp unit, not the rubber seal.

The tailgate is built with an internal scoop to deflect any water that leaks in, down into the base of the tailgate, where it exits via the drain holes, but fails to catch water that runs inwards down the lamp unit.
My observations are that most XM tailgate liners show rust staining, especially round the latch mechanism and have evidence of water. I am now confident this water intrusion is from the lamp unit seals.