Another major disaster!
So I went to start attaching the parts to the top of the playfield today and noticed, to my horror, that the automotive clearcoat used was not as hard as I was expecting. Under a couple of the posts I had already attached, the clearcoat had started to wrinkle up:
Clearcoat which has been squashed out from underneath the post
There is nothing I can do about this (apart from loosening the posts to prevent the wrinkling from getting any worse) and also to make sure any other posts aren’t secured as tightly.