I had a 530 with the Case-o-matic. No problems either with the trans, although I was told at the time torque converter's were pretty expensive. For kicks, I looked for a used one, and that time (15 years ago) it was $1800.00. One thing to remember, they are like most tractor of the era with Torque Amplifiers systems.. They will freewheel when in the low side, when going down a hill.
Just guessing here, but I'd bet most reasons why the torque converters went out, was from using it as a braking system, when freewheeling too fast, and shifting to lock up the torque converter.
I'm thinking that would have been a great tractor on a 3 pt. tiller.
Brake seals seemed to be a problem of that era tractor too. The disc's can be cleaned up by boiling the oil out with a propane torch, and some brake cleaner. Seals locally are about $15.00, but I found a place to get the same CR seal for about half that. Just takes a week to get them. And getting the seal over the splines without ruining the seal seems impossible without the proper tool. But through another forum I found out, wrapping the splines with electrical tape, from the inside outward, and coating with oil works great..!! Plus the fact you only do one side at a time, or the pinion shaft will drop. It pays to have a good shop manual..!!