they will more than likely get a used rear end...hard to say, but it wouldn't be 'brand new' it would be rebuilt probably...but I've seen it where we got some used diffs if it was off of a beater...long time ago...

I wouldn't try getting the diff replaced; your issue is well documented here and the risk just isn't worth it--fraud is a lot bigger problem than a bad service on your diff--call the manager and tell him you want it done right. Could be a Jiffy Lube person on here, ya know.