Front derailleur rubbing against chainring I'm trying to fix up my old (1999) Trek 4500, and I've run into a snag while adjusting the front derailleur. It's a Shimano FD-CT92 (bottom bracket mounted E-type), and it's rubbing against the largest chainring when it's in the middle gear position. There doesn't seem to be any height adjustement on that type of shifter. I've checked all the documentation I could find, and the chainrings are within spec (42T, 34T, 24T). In any case, all the equipment is original to the bike, and I've never had this problem before.... Any ideas on how to fix this? 

Here's some additional info:

This is what the derailleur looks like when it's in the middle chainring position




The FD-CT92 derailleur is bolted to the bottom bracket plate in a way that prevents any height adjustment. A flange that fits around the seat tube also keeps the angle fixed.

(the photo below is with the derailleur detached from the bracket plate)



The only other thing that I've noticed is that the cage can be wiggled around a bit. Is that normal? Do derailleurs wear out?
bottom bracket has come loose slightly allowing the plate to turn.