I had real issues w/ my stock 440/505 seal, ended up finding the rear seal cap was machined off center on the \bolt holes , was off center when bolted down , none of the above would fix it !
I've noticed that most of the seal retainers are not centered, this is the entire issue IMO.
By using alignment pins and dropping the cap over an offset seal everything automatically lines up. The gaps between the block and the seal retainer are usually greater on one side over the other. If you try to center the retainer in the block with the seal ends flush the alignment can easily be off enough to leak.
