I have a Giant MTB that I use for a daily 30 mile round trip commute. It doesn't like to down shift so I replaced the chain, replaced the shifter cable, and adjusted the derailleur. The Derore rear derailleur seems to have play in the area where it bolts to the dropout (hanger). It feels like it is loose but it isn't. I thought it may have a worn bushing. I have a used Ultegra 6600 rear derailleur and was wondering if it will work on a 7 speed MTB. I don't see why it wouldn't work but I thought I would ask. Thanks.