Please post Model Number, Spec Code, and Serial Number.
If it's in the "4KY" series, it's a lot like a small mower engine. Splash Lubed, No Oil Pump, No Oil Filter, and unless ONAN has put it back, NO Low Oil Sensor. 4KY's had them for awhile (the lower Spec Codes) but discontinued them.
A replacement "short block" for them is not as expensive as you might think. Far from free, but at a few $ hundred, better than a new genset. Then there's the labor of changing it. The OP who posted here, ordered the engine and did the labor himself.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB