[PetChemMan]

More often than not, valve cover gaskets leak because the stamped steel covers become deformed around the bolt holes. Before you reinstall them, use a straight edge to be sure the surface is straight, and hammer the area flat around the bolt holes as necessary. I also agree that using a sealer on the valve cover to gasket surface makes installation easier. However, it may also make the gasket more likely to slide out of place when you tighten the bolts, so take notice of that. ( And, in accordance with Murphy's Law, the gasket will invariably slide out of place on the bottom of the valve cover where you can't see it !) Using a high tack sealer such as Copper Coat helps.