Rubber gasket vs. a cork gasket

Partly depends on the type of valve cover you have. If you use covers with a flat bottom surface without the outer lip to contain the gasket using a rubber gasket is like trying to pick up jello... I find the rubber impregnated cork gaskets work the best for me - and they are cheap. I use a very thin layer of sealer on the valve cover side just to hold the gasket (let it set up good with the gasket on before putting on the heads), and hand tight plus ~ a quarter turn to start. Let it set over night and put ~ another 1/8 a turn on before running the motor. This method finally has my current RB with Indy heads dry for the first time since I bought it 3+ years ago - and I think I have tried every gasket/combo on the market..