changed the plugs 2000 miles ago and 1 plug was oil fouled, so I checked the compression- the #2 cyl was 125 and the rest were 150ish. I was replacing the valve cover and exhust gasket yesterday (leaking), so I pulled #2 and #4 and this is what I got- #2 on the left. How do I test the valve seal/ piston rings? Could that have happened from leaking valve cover gasket #2 plug did have oil on the threads? Can I drive it this way or will it kill other parts? So many questions from a newbie? thanks for the help!