Store brand oil
I worked for a large oil company in R&D and the oil company did manufacture engine oils for many chain stores. In order to make the oil for a cheaper cost to consumer the additives were cut back, anti-foam, anti-oxidation and so on. The oils met ASTM and other specs required but at the bare minimum. Use a good brand name engine oil at all times and it will pay for itself in the long run.
We had engines come in for analysis with all kinds of sludge in the oil pan and scoring on cylinder walls, valve problems etc. from using brand 'X'.
Dennis and Lorraine, old at camping only: