Before Marvin sets the crank, he gives the rear main seal grooves a dressing of Permatex's The Right Stuff to ensure a good seal between the block/cap. Marvin will tell you the whole point of a gasket is to seal, adding that many builders overdo the sealer. Just a thin film of The Right Stuff is necessary. Don't forget to remove the original rear main rope seal pin if it's still there. Otherwise, it distorts the rubber seal and you will have leaks.