I had a front cover leak there once on the dyno, so we took a high powered shop vac and taped the hose to the valve cover breather, taped the other valve cover breather off, and put silicone on oil pan/timing cover seal and let the vacuume pull the silicone in good. Worked like a champ that time anyway. Just dont get carried away and fill the pan full of unneeded sealant!