I ordered everything from BPI Inc. Cost and delivery was much better than anywhere else. Below is a post from the past....
Ted, I have the same engine and transmission, and had the same slipping 2 seasons ago. I bought the clutch plate kit and the gasket kit from Basic Power Industries, about $320 US. I have a friend that is an auto mechanic, he rebuilt it and I have had no issues since. The clutch plates were very polished, after only 500 hours on the engine.
Part #s were
ALT316750 - Clutch plate kit for Hurth HBW 5, 50, 100
ALT316801B - Gasket set to Overhaul Hurth HBW 5, 50, 100
Still running as good as new.
Cheers
dj