I've got a 580B case, runs good, shifts good, just split and put a new ring gear on the flywheel back in early spring and resurrected after sitting idle for about 6 years. Now, the hoses all need replaced, and the cylinders all leak, some worse than others. Kinda rough looking but functional. Guy close to me has one for sale, for 4K, runs good, no leaks, in better cosmetic shape but says it "pops" out of reverse.. when I asked him when it comes out, he said as soon as you put it in reverse, it comes right back out. Question is, if I buy his, how hard would it be to fix that using the one I have, I then would have everything else on mine for spare parts.
I hear this is a cronic issue with the 580bs, mine pops out of forward quite a bit , not so much in reverse I can feel it go into and out of the detents when I go from forward to reverse , plan on pulling the cover and looking into it further , someone on the forum suggested a worn woodruff key on the shifting arm , I do not feel any slack in mine but it could be. If I find a solution , I will post though.