yeah if you're not following some of what i was spitting out, don't get into the repair unless you want to play one day and learn a lot
as in you don't care if you trash the old one. can be fun if you're into it.
yeah getting another lsd and swapping it in is by far easiest/cheapest. as syris said, as long as its good. the problem with that you will probably have to hunt around at scrap yards to get one and there's no guarentee that that one won't have similar problems or even worse problems.
i got one for free off a friend so it wasn't such a big deal that my second one sucks too. they'll usually go for a while before the bearing completely gives out, but be warned when they blow it can be sudden, major and dangerous. for example, the gears can mesh their teeth and lock up. i've seen pics where a guy cracked the housing and that thing is solid cast iron!
that being said, if you have a bearing whine and it isn't overly loud i wouldn't go nuts trying to find a new diff immediately. they're really quite tough.
most mechanics don't want to do the swap as its part of the drivetrain so they like to send you to a transmission mechanic. up here in canada it cost me about $350 with taxes for the swap
you may also have to get oil seals replaced if the new diff has been sitting around for a while, but those aren't too bad price wise. about $25 CAN/seal here and labour is quite minimal. could even be under an hour per seal of they're good. but first things first. start calling scrap yards