Shimano Front derailleur I am rebuilding a Trek 2005 model 6500 and my spec. sheet for the bike says it has a Shimano Alivio front derailleur.  Where do I find the model no. that should be stamped on the part? I don't see it anywhere on the part.  This is a 3 x 8 speed setup.

Thanks,
Jerry
You might have a hard time finding the exact same part that was originally on the bike. However, front derailleur is a pretty standard piece of kit and you can replace it with compatible. 

Things you need to look for when buying front mech:


Road and MTB FDs are different
Shimano and SRAM FDs work with the others shifters (which is different for RDs)
Seatpost clamp diameter - size of the tube the mech is clamping around (Shimano FDs often come with shims but SRAM FDs do not)
If the mech is top pull or bottom pull: the cable comes from above the derailleur (top pull) or below (bottom pull). Dual pull derailleurs work either way.
There are 3 clamp positions: high clamp sits above the mechanism, low clamp is at the same level of the mechanism and e type is on a frame which sits between the bottom bracket and the crankset.
Make sure the new mech is 8 speed. 9 speed-mech won't work with 8 speed chain, as the chain widths are different.