Steve ,we just recently finished building my engine for my Kirkham. My builder used the 2 piece rear seal, staggered it in the cap, squeezed a good amount of RTV into the side seal area before pushing the side seals in, even smeared a little across the back of the cap mating area before putting the cap on. Haven't dropped it in the car yet, but numerous hours on the run in stand and a long dyno tuning session and no leaks yet.
Hopefully you can get yours to stop as well.
Oil in the bellhousing is just following inertia while moving down the road, it tends to track rearward, probably leaking just at the rear main since it was inside the bell housing.
Is your block a cast iron factory side oiler? How's the pan mating surface near the cap? Are you running the sandwiched factory windage tray?
Curtis