Cork gaskets are the only ones I use, and the only ones I could ever get to seal. Silicone the gasket on the valve cover side, and snug with a nut driver. Not so much as a seep!

1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)