Well, mine blew up!..lol.! They do go out eventually, they either start to slip, (wear), burn up and die, or explode. It just depends on how hard they were driven.
The ford LS is nice when new, and if it is in good shape. BUT nothing compared to a locker! A locker will take you farther than a LS ever could! Lockers are the things wet dreams are made of boys!
Yes, your door tag will tell you what it came with from the factory. But, it could have been replaced by a previous owner, you never know. There is a alum tag on the diff cover as well, it will say what it is also, BUT, I don't trust that either. It could have been from the old rear end if someone swapped it out. I know this seems a little paranoid, but when your talking about spending hundreds of dollars, it is not hard to open a diff and have a peek to make sure.