Check that there's no play in the stump jumper. Some gearbox play is OK, but not excessive play. Pretty much sounds like a decent deal.
I bought an intensely used Bush Hog BH26 for $800 (just don't find 6-footers for sale around my neck of the woods). I had to buy a new PTO shaft for it: went with a really nice Bare Co one. That was a few more $$s.