pull plugs and look. jugs pumping will be black and shiney and fouled.
anti foulers can help..and I like 15w40.. but as another poster said. i just use it alot and have it on hand.
if only 1 lung is pumping.. might be broke OC ring.. might pull hed and pan for a re-ring, cyl hone, ridge ream and new sa,e size bearing shells.
likely pick up some compressiont and il pressure.
maybee even hand lamp and reset valves.
cheap po-mans in frame..