Not leaking oil
Suggestions for oil?
You said it doesnt leak oil..that doesnt mean it doesnt consume oil...
I would start out with Walmart or Costco or whatever 10w30 is the cheapest and monitor consumption before going with a higher cost oil.
Im sure you have looked it over nicely.. have you started it while cold does it smoke? Have you Pulled PCV while hot to see if it has blowby? Tailpipe soot?
Long test drive with multiple stops for CELs?