While not an expert in oil I’ll pass along some hints, tricks, and concerns I learned (heard) over the years.
1)You should run your engine at operating temperature for a period of time, not just bring it up to temperature and shut it off. This allows the extended heat exposures to evaporate any moisture in the oil before changing. This is why short driving trips are harder on an engine than longer commutes
2)You should not let any oil sit for long periods of time once the oil has been run, even for short periods of time, as it develops acids and other heat related changes that can damage bearing surfaces and other metals. This can be seen as pitting of machined metal surfaces. Once you’ve identified the end of your season you should change the oil before storage. If you continue to run the gen on a regular bases (at least every 2-3 months) then change the oil at the recommended intervals.
3)Always change oil and filter to remove any particles of worn metals and the acids contained in the oil.
4)Additives and supplemental are your call.
Hap