It MAY be the circular gasket that seals around the camshaft.. but im really not sure.. This gasket/seal is constructed of a rubber ring, with a circular spring that applies a small amount of pressure, i know when i did the head in my car, both the spring and the rubber in the seal were pretty worn out... When you replace this dont just push it on,, the rubber can fold in and the spring will pop out.. and if your not careful you can lose the spring.. What i did was, i lubricated the circular seal before installation, then i placed it square against the shaft,, then i took a toothpick and slowly ran it around the shaft while applying pressure to the seal,, and it slide on fairly easy. but pushing it right on will result in a possible lost spring, and you will need to buy another seal... here is a picture of the POSSIBLE problem below