So, mechanic confirmed that it is a ZF transmission (no surprise there) and he has seen a bunch of these (in fact, was just finishing another one up today).
Quoted me $3200 for a new one (I think that is installed, but can't be 100% sure till I talk to him again). He's looking for a used one now.
Nuts. My old e28 hit 205K needing nothing more than a busted fuel line and new bushings (beyond the usual brakes, tires, clutch, exhaust, etc.) Never should have sold that car.