The rubber ones are the only type I will use. They have some compression to them, and I feel that can seal some irregularities in the head. When I remove the valve cover they are still soft, the cork dry out and become hard. -Smoky Mt Frank- In a message dated 3/29/2010 12:52:40 P.M. Eastern Daylight Time, elcam84@xxxxxxxxx writes: The only ones I like are the rubber ones with the steel insert. Felpro has some good rubber ones.