I slowed the doors down to a moderate crawl and added the smallest drop of oil to each pivot - virtually no jerky movements at all now.
I’ve also been thinking about the slight warping of the shed structure. I don’t particularly want to build a new one and to get a similar four lane shed would need modifications to at least two Bachmann NER sheds (megabucks) and I’d probably have to change the rail spacing as well - so that’s unlikely to happen.
My thoughts are now turning to removing the roof as a complete unit (I don’t even know if that is remotely possible) then warming the resin walls and putting some tension on them to straighten them out.
If I can get them level, I can fix them permanently to the baseboard and the new door frames with a removable roof for track cleaning and stuck locos.
I just need to work out where to make the cuts.