To close this out: I decided to pull the trans and ship it to Nassau instead of going there. After originally saying there wasn't anything wrong, they finally consulted with ZF Hurth
and replaced the cup springs and thrust washers. It's back in and feels strong now, so hopefully it will hold up a long time!
RE parts: looks like springs, clutch
disks, seal kits are all readily available. Gears, bearings, not so much.
Thanks for the suggestions and help, all!