Best sealing valve cover gaskets

You should be able to set the valve cover on the head without the gasket and have it touching the head all the way around. Try that and look through the holes to make sure it is seated all the way and not hanging up somewhere. A normal cork gasket should work unless something is screwed up. Put a straight edge or ruler on the cover rail and make sure it isn't warped.
The factory steel unit deffently wasnt flat, I removed the drivers cover (aluminum) and just look at the oil on the head surface...I'm checking them now

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