For decades I have used the oil that I drain out of my automotive engines when changing the oil. I have also used transmission oil, gear oil, anything that was removed from the cars during a lube change. 'Never seemed to make any difference in the longevity of my chain or bar. It's a chain saw for sake. It gets into the dirt and muck. Maybe a thin oil helps the crud get thrown off the chain better, less particles to cause wear?
All my saws got a lot of use after this hurricane IAN a month ago. Dealing with 10 trees down, big ones, still working on it. 'One thing slowing me down is my Tennis (chain saw) elbow that resulted from my old age limitations.
ali