Onan stopped supporting the pre-cummins merger gensets, and parts are no longer available. I went through this on my last boat, and the bottom line is you just need to replace the generator. I would scour the internet and would eventually find whatever the part was from some obscure fishery supply place in Alaska, some guy on craigslist who was removing an MD model, or something equally one-off, but then a few weeks later the next thing on it would break and it would start all over again.
Out of any given 12 months, that generator may have been working properly for half that. It was really making me hate the boat, because you couldn't run the a/c's, cook anything, etc. Wasn't worth it. I replaced it with a 12kw Phasor and never looked back. I put like 600 hours on that thing with nothing but an oil change and never had the first problem. Onan makes a crap product anyway compared to Northern Lights, Phasor, or any of the current options, in my humble opinion. The former owner of my hatteras went through the same thing with the one in this boat, and replaced it with a Northern Lights. So far I've had to do an exhaust elbow, a water pump, and an oil change in like 300+ hours. It's no comparison to an Oh-No!
