So my sons car 1990 300e m103. Uses a lot of oil leaks everywhere as well as fouls the plugs. So recently it started running rough and we removed the plugs and cleaned them. As well as inspected the cap and rotor. Then it ran good again for a while and now its running rough again. Could be the change in weather but who knows. So I pulled it into the shop today and started trying to figure something out to fix. I bought a spark tester and checked the spark at all the plug wires and they all had good spark all the way to 20mm. Then I did a compression check, but the engine was cold and I did not hold the throttle open. all 6 cylinders were 125-130 ish. I added some oil to each one but unfortunately I did not use equal oil lol Some went up to 175 some went to 150. Then I hooked air up to the cylinders this is were I got really lost. I took the valve cover off. Then I had all the plugs out and I would rotate the crank to where the valves looked close and then open the air up. The air would then either come out the intake breather hole or come out another spark plug hole. So then I put the plugs back in and did the test. I think the intake valve was opening from the air pressure so I would turn the crank with the air on until it stopped. Then the cylinders were holding air with no leak. Not once did I hear air coming from the dipstick tube. Did I make the mistake of doing this test after I put oil in the cylinders? Should I put some acetone/atf mix in the cylinders and let it sit? At this point the valve seals look like a really easy job, but I dont want to just replace things for no reason either.