I live in Seatac Washington but can deliver the engine anywhere between here and Moses Lake, WA (where I will be working in June & July.
I am not sure of the name, but it sticks in my mind there was a place in Moses Lake that did Onan Repair. The best I can offer you is call Cummins NW (preferably in Yakima) and maybe they can give you a name of someone still doing Onan repair in the area. You can also check with Cummins NW in Renton, which is near you - bper
PS - The guy in Moses Lake may be retired now, like me.
Retired Small Engine Technician .....