Now I'm thinking, how long since that valve cover has been off, or the clutch cover for that matter, because the only real way for that to get there is if both were to be off at the same time, and if it's been a long time then you would have had problems long before now,,,, I'm thinking,,,,,, PO took stuff apart, lost the plug, then found another and put that in,,, but then I was only thinking and that doesn't always work the best, but sometimes even amazes me.