Thanks everyone!
After looking around a bit it seems that synthetic is pretty acclaimed for these motors, so I went ahead and just stuck with it.
I have heard about the #6 exhaust valve getting burned out, my guess is the valve clearances have probably never been adjusted on this one. It runs nice and smooth otherwise, doesnt have much power of course but it doesnt seem "weak" by any means.
I assume a compression test would point out any issues with the valves?
