Thanks for all the advice and ideas. Mateoruiziii has one that he says is in good shape, so I'm going to try to work a deal with him.
What's wrong with the current case I think is just a stretched chain, but without opening it up its hard to know for sure. It still runs OK, but makes a racket that's getting steadily worse, so I wouldn't trust it on a long trip or offroad. I'm going up north next week to do some turkey hunting, and will most likely be using 4 wheel drive at times, so I need to have everything in good working order. If mateoruiziii's unit works out, I'll probably rebuild the old unit eventually and keep it as a spare.