I've had great success in the past with the Felpro rubber gaskets. I use them alot on solid lifter or roller lifter engines. I've reused them continually for a whole season without a leak through many valve adjustments. If using the cork gaskets where you don't need to adjust valves I suggest gluing them down to the valve cover rail with 3M black weatherstrip adhesive. Yes the same stuff used to put on your door weatherstrip. Lay a continous bead about an 1/8 inch wide all the way around the lip. Let it set up for about a minute then lay the gasket on. Once in place gently lift the gasket up about an inch a little at a time all the way around the cover to "string out" the adhesive. Press firmly in place and let it dry until you can't move the gasket around on the cover. Lay an 1/8 bead of black silicon around the gasket for some extra insurance and reinstall. Torque the gasket snug and do not over tighten. The glue holds the gasket in place and won't allow it to split while tightening. If done properly this method has NEVER leaked, guaranteed! You can do this with any gasket that contacts oil except head gaskets. Good luck!