"Real Gaskets" makes a silicon set, but it's not one piece. I also have tried one of their valve cover gaskets which leaked like a broken dam at their light torque spec. I tightened past their torque spec and it leaked less but nothing I could do stopped it. Yes, I straightened the valve cover perfect before I swapped to it and I also removed the valve cover and checked the valve cover rail on the head with a straight edge. The valve cover rail on slant sixes is a machined surface, so it was perfect. I swapped back to a tried and true cork gasket and all is well. I threw that other crap in the garbage.
