i dont know what to look for its pretty hard to actually see any damage because on something like that a piece of metal that has even worn down a few thousands of an inch could cause it not to grab. if you rebuilt your transmission (2 of 3 getrags i had were fresh rebuilds) and after i had them rebuilt it made the top cover 10 times worse. i dont know why it did but probably because everything grabbed better in the tranny it would make the upper cover looser. i cant tell you how to trouble shoot if thats what is bad with it but its my best guess. maybe take the cover to a transmission shop and ask them?