For about the last three years or so we have been using a one peice rear main seal in the 351W block that were two peice. We machine the blocks for the one peice seal to try and eliminate the rear main seals problems. I know that on a lot of the Superformance we have had the front
oil pressure line leak at the block and run back. Remember any leak you have will run back to the center of the trans cover and look like a rear main leak. Double check all
oil pan bolts as well along with any drain pliugs or fittings. Good luck, Keith Craft