I recently replaced a set of valve cover gaskets for a buddy due to an annoying oil leak. The passenger side was obviously leaking because of the brittle and cracked state that it was in. The drivers side looked not as bad and was replaced. We sat back cracked one and fired it up to check our Sunday afternoon job. The valve covers are sealed but we still got an oil leak on the drivers side. At the back of the block just above the oil cooler lines. It is coming from between the head and the block. If you take off the oil filler cap it almost stops. It appears to be only oil and can't smell any fuel, no external anti freeze leaks and nothing in the pan. The CDR tested OK with a manometer. The engine runs fine and a comp test didn't find any dead/low cylinders. Is this a good sign to pull the heads or some thing that's not to worry about?