I have had a rear mainseal leak since day one , I have finally found out why, after 3-4 times trying to fix it . The main seal cap is not made right, or the bolt holes in the block are offset from perfect, or the crank is setting in the block crooked . Don't think it the crank cause all pistons were exactly the same deck heigth when built , if crank was crooked one side would be off , compared to the other side. I installed the main cap after cleaning it up w/o the side seals , letting it center itself on the crank , ( no bolts) , one side of the cap is way closer to the block than the other side . I redrilled the bolt holes out bigger and checked the bolts , they (allen heads) were .005 bigger than stock , slightly adding to the problem. I still haven't figured out how to seal the cap on the sides , w/ the engine in the car , getting the whole mess clean of all oil would be a bitch , not to mention how to get sillicone up in there to seal it from the outside. I have found a billet main cap that is offered by an old funny car racer, and not like the current ones on the market, ordered it this morning. If its the same way , sealing the sides will be a bithch , 73 yrs old and laying on a piece of cardboard in the floor aint fun any more ! Sorry for the long rant m "more to come !"