Clean both surfaces with brake cleaner or similar solvent. Glue the cork gasket to the valve cover using good quality RTV. Let sit lightly compressed overnight. Then coat the otherside with wheel bearing grease. Attach the valve cover to the head. Uniformily tighten the vavle cover bolts. If you ever have to remove the valve cover again you can still reuse the gaskets. Give it a try then tell me how you like it.
Good talking with you Allan.
Morgan