In addition to what's already been posted, try to talk to the guy/gal who's actually doing the work...lotta times your description and/or requests will be passed down 2nd or 3rd hand sometimes, going from your contact at the shop to the new kid who's actually doing the dirty work of diagnosing and replacing your front differential
. First hand is always best...personally that's why I prefer a local 4x4 joint to the dealership, because the guy at the counter is probably the same guy who's doing the work.
-Sean