Inside Roof Trim - any ideas?

[andreoz]

A few months ago I noticed that the section of roof trim just above the rear window started to slip out but it was just a matter of using my fingers to plug it back in and it seemed to stay there for a while. It is now getting a lot worse and when it slips out more and more of the fabric gets lose to the extent that it can be affecting visibility. Any hints as to how to attach it permanently. It seems that the fabric is detaching itself from the solid section of the roof trim. How is the fabric stretched and moulded over the solid section - is it done with some form of heat treatment. Any advice would be welcome before I have to take it to a car trimmer.