I've dismantled one of these, and I don't remember anything that would hold it in place after the dismantling you have carried out. Have you slid a knife blade all the way round and across under the top plate in case some hidden Vulkem is still attaching the plate to the roof? Just a thought.
on edit- too late, by three minutes! I'm glad you sorted it.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."