The problem isn't the gasket, it is the valve cover. Or possibly the cylinder head depending on which head you are using. Factory cast iron heads are horrible for leaks, aftermarket aluminum head typically have a machined rail and shouldn't leak. Factory steel valve covers are almost impossible to keep from leaking as are many of the cheap valve covers on the market. High quality valve covers don't leak regardless of the gasket used. Cheap valve covers will leak regardless of which gasket you use. I fought valve cover leaks for years and then finally figured out the solution and now I never have any leaks.
