I have the 440source covers on my engine. They don't have any leaks after 5 years. Only problem I have had with them is the baffle under the vent hole fell off on both valve covers. Also if you are running an MSD distributor the valve cover will need to be clearenced a bit in order for the MSD unit to fit properly.

I just put a little heat on it and used a body hammer to put a small inside facing contour and that seem to fix any problems.