I haven't had the valve covers off on the Contour yet, but on my SHO there are rubber seals that provide a seal between the valve cover and the spark plug well in the head. These seals are notorious for leaking if left untouched for too long, typically 100K miles or so. When they leak, the plug well fills with oil causing all kinds of drivability concerns due to misfires, etc.
Bet yours has the same problem.
Steve
