Is that a cork gasket on the valve cover? Cork gaskets are shit. Buy a FelPro rubber gasket, like one of the nice ones. I forget what they call them. It's like a problem solver or something like that. Molded rubber, not just die cut. PermaDry! That's what they're called.
https://www.rockauto.com/en/parts/fe...r+gasket,10710
Not 100% sure that'll fit. Says 86+