[SuperHart]

There is an outfit called DSC Motorsports that sells extra thick cork based valve cover gaskets for the FE motor. They are much cheaper than the ones you show from Summit. The link is http://www.dscmotorsport.com/ I recommend their use with the valve cover adapter kits I sell and they work quite well. If you are using cast aluminum valve covers on a FE motor and are certain that the gasket mating surfaces of the covers are perfectly flat, usually any gasket you use should produce a satisfactory seal. The usual place for leaks to occur on a FE motor is at the joint between the intake manifold and the cylinder head. In most cases, a dab of Permatex UltraBlack silicone in each joint prior to applying the gasket will solve that problem assuming that the intake and cylinder heads are properly aligned to begin with. It might be of interest to know just where along the valve cover the leak is occurring. Lastly, using studs instead of bolts to secure the valve covers along with spreader bars might also help.