I am trying to install a rear main seal in an aluminum /6. I have no issues with the two piece neoprene seal and side seals. What has me puzzled is how does the top seal retainer seal against the block. Seems like it would require something such as sealer or gasket to keep it from leaking (like the bottom retainer). The block mating surface has a groove in it but the retainer is smooth. The service manual and Doug's article make no reference to it.