I'm replacing the stamped steel valve covers on the 350 with covers from an '84 'Vette. They're made from magnesium or aluminum and are thicker than the current covers. My question is "Is there a preferred gasket material for these (cork, rubber, silicone) and is gasket sealant needed or required. I've researched online and it seems to run the gamut. I only want to do this once and hate going back looking for leaks. Any previous experiences or knowledge is appreciated. Thanks.