Joe,
As you know, the old Onan parts are getting to be impossible to find and Onan/Cummins has no interest in supporting the older units.
This is what caused me to buy a brand new generator about 5 years ago when a small $150.00 gear went up on my 15kw MDJE. No one had the part new or used. I located a couple of junked gensets but the part we needed was gone. I looked into having one fabricated at a machine shop but the time it would take was not acceptable - our season is too short as it is.
Ended up pulling the Onan and sound shield and installing a new Fischer Panda 16kw. Sold the old genset and sound box. It was very painful to spend the $$ but we were up and running in about 10 days and the new genny is much more quiet and smooth. We even got the outfit doing it to do all of the work through a single engine hatch so we didn't have to tear up the salon!