I used to find that glowplugs were needed always, hot or cold, summer or winter. It's a design feature of the Indirect injection system used on the XUD engine that preheating is always required to heat the air in the pre-chamber to ignition temperature as the main compression provided by the piston won't do it.
An XUD with four duff glowplugs is incredibly hard to start as this video shows:
Poor 405

In fact it's remarkable it started at all and this video shows how important post-heating is too. That's where the glowplugs stay on for several minutes after the engine starts..
[youtube]4xs4TBHWq9k[/youtube]
Russ, I believe the big problem with the filter head is the priming diaphragm - the bit behind the priming button... I've not had a lot of experience of them unfortunately so can say no more than that.