I have 540 hours on Onan 4000 in Vegas. It get oil change annualy with 15w-40 conventional per manual. Is 6 years old. No issues or oil use so far.
All my other air cooled equipment use the same oil. The 3500 champion on race car trailer I bought week after RV probably has over 5000 hrs now. I have had to replace starter twice due to broken spring but it still does not use oil.
Key to generator life is oil changes and keep linkages lubed.
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