I have had great success with the cork Felpro gaskets. I use RTV silicone on one side of the gasket, and put it down on a dry/clean surface of the head. Then I put the valve cover on. A lot of leaks are made when people over torque the valve covers. They don't need to be reefed, that's what distorts the gasket and causes leaks. I just tighten to lite tension and stop. This will eliminate that dreaded oil on the X over pipe.