[Paul F]

A cast aluminum cover is a good thing. Chances of the seat being distorted are low.

If you have gasket sticking out:

-it slipped out of place while you were installing it. I find that studs are not spaced close enough to keep this wobbly thing in place. That's why I use just a thin film of silicone to act as glue to hold the gasket on the cover. Chances are this is the problem.

- you're tightening the valve cover down too hard. Chances are, this is not the problem.