Ericson 32-3 Transmission Problems ZF10

I posted in 2010 re replacement of my transmission which was persistently slipping out of forward gear. Replacement unit was a Hurth ZF10, I believe a rebuild (my notes are unfortunately skimpy). The new unit has now developed the same problem and the recommendation is replacement.

The yard is saying that the ZF 10 is no longer available, and that they would put in a ZF 12, which is larger and may require shortening the shaft.

Questions:
a. Does anyone have a line on finding a ZF 10?
b. Are there alternatives to this type of transmission that may be more reliable and are not so large as to require shaft modification? I'm finding that the Hurth reputation is less than stellar.

I had a Hurth transmission in our E30+ which slipped without warning. I think it was the smaller ZF 50 (or 5?). Mechanic recommended replacement with aTwin Disc MG340 which did not require any modification. I have had it for 8 years, and while it also slipped a few times in the first few years, it has not done so in quite a while and seems good. As a precaution I change the transmission fluid at every oil change (about 75 engine hours) which is much more often than the transmission manual suggests, but it's fairly easy to do and might be partly responsible for no problems now.
Frank