Are you running the valley pan only or with gaskets? If pan only I would remove it and get some adhesive silicone sealer and plug the corners wih it so it will ooze out between the head gaskets, vally pan and the front and rear block sealing surfaces The sealer needs to say Adhesive sealer on it to seal up with the engine oils of today. Some guys are having excellent luck with the Permatex Ultra gasket sealers also IHTHs