The C30 yahoo group might help you out. The C36 skippers have had remarkably numerous
transmission issues, but usually on the later engines.
www.catalina36.org
The C310 group with M25XPAs have also had issues.
CatalinaOwners.com - Home, find their tab under the Forum tab, upper left.
We simply haven't had those issues, but feel free to look around our C34 tech wiki: Engines 101 - The BIGGEST & BEST collection of M25 Series Universal
Engine Information on the
Internet, plus some M35, too
Diesel Engine - C34
The key seems to be, in a
rebuild, the type of replacement
clutch material you get.
The larger ZF10 fits, IIRC.
Good luck.