That is alot of work. One other item to check is the 120VAC output power wiring. The Genset has a circuit breaker which is for overloads. Only.
Check the wiring where the sealtite conduit comes into the genset and make sure all the connections are secure. This same sealtite goes to a junction box somewhere on most of these and then to the house (YMMV). check the connections there also.
Motorhome back I had the same problem where the factory did a poor job wiring the 120VAC at the junction box mounted on the frame and the wire nut on the hot was loose and eventually fell off. When bouncing down the road in the summer with the A/C on it hit the grounded box intermittently. Never at other times. Inside of the box was black so it was arcing but ran fine.
What it did was cause short sharp surges back to the genset, the Magnetic breaker on these will not trip under this type of short duration spike. It caused the excitation field brushes on the generator to foul and pit.
I found and repaired the junction box but the next year the genset did the same as yours and the code on that was no power. At that point, removed it and took to service and $1000 later had it like new. Carb, rebuild brushes and gen side, controller, pump.... At that point it was about 5 years old.
Good luck.
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