I have a 2004 Mach 1 but Im posting this here due to heavier traffic to this sub-forum, and the similarities between the motors (heads specifically). I changed my spark plugs and COPs this AM and found this on cylinder 8 (firewall/passenger). In addition, there was a tiny amount of oil on the face of my socket head when I removed the old spark plug. I also found this odd build up inside the COP seat on the valve cover. What am I seeing here? Valve cover gasket? Piston ring? What is the most likely cause of this? Details on car: Bone stock internals. CAI/x-pipe/cat back/mild tune. Makes 317/320. 25,017 miles.