Sometimes when we buy "used" parts we are pleasantly surprised. Sometimes we're not. In either case that's just part of the hobby and you have to be prepared to deal with it.
I disassembled the Ford 9" I bought for the deuce the other day. Bought it about 10 years ago from a guy named Rufus somewhere in BF Ohio. He lived so far out my wife said it was a wonder they actually had electricity.
The rear was out of an F-150 and the tag indicated it was an open carrier with 31 spline axles and 3:25 gears. The original plan was to re-use the gears and carrier and just slip in a Detroit EZ locker. I had hoped to avoid all the time and effort having to set up the rear with a new carrier and gears but that's just not going to happen. The rear had been sitting outside too long before I bought it and moisture had attacked the ring gear.
My first clue was when I had to cut off the drums. They were rusted on the axles but interestingly enough they had not rusted to the brake shoes and turned freely. Here's what I found when I finally got the drums off. Everything coated in a nice patina of rust. The good news is that it's all salvageable except of course the cylinders, shoes and springs.
Took the housing down to the local car wash and gave it a good hose down with high pressure grease remover and that cleaned it out very nicely. Now its ready to have the spring mounts, shock mounts, and all the surface rust removed. Then I'll be using my new jig to narrow it to the proper width for the deuce. Stay tuned.