I highly recommend you cruise over to:
https://www.smokstak.com/forum/forumdisplay.php?f=1
For Onan help.
They are not very hard to work on once you get them out on a work bench. For me the thing was a black box until I determined I was tired of dropping $500 every time it needed service.
Turns out my old 4BGE you can replace every electrical thing on it for less than $200 (starter, plugs, ignition control module, distributor, condenser), and you can replace the voltage regulator for $150 and the control board for $200.
The engines themselves are pretty bullet proof given how little they run.
The Achilles heal of my genny is the little plastic propeller they put on the main shaft in between the engine and the gen head. This has the magnets on it that the ECM picks up. If a mouse builds a nest in there and you try to start it, it will shear off the rotor arms. It has not happened to me, but if it does you have to split the genny in half to fix it.