Originally Posted by
liampboyle
Honestly I just don't know. I was looking for a model # earlier but couldn't find it. I bought the bike used from my LBS.
The model number of the rear derailleur should be on the inner linkage plate. It should start with "RD", and would read something like "RD-M737" or similar.
Edit: or,
here is the 2008 XT group. Does your derailleur look like one of them (and, if so, which one)?