Thanks for the comments and suggestions so far. Yes, it looks like 4 screws and the collar ring will get the top plate off but man, that collar ring is hard to get a grip on. Having said that, with a closer look, that ring has seen some past action (scratches, grip marks) so while I've not dropped the camera, perhaps this is not an isolated incident.

Repairman it may have to be since I just got it. Not had much luck with my last few used gear purchases.