When I replaced the gaskets in my car, I used a new pair of Felpro Rubber gaskets. I'm not sure but I think there's a specific sequence and torque rating for intalling the studs on the covers. If you tightened them too much, you probably crushed the gasket, causing it to leak again. I've heard of people who use RTV in conjunction with the gaskets, which apparently works just fine. Maybe someone more knowledgeable will answer your questions definitively.