True enough, there is no actual rear seal. There is a ridge at the back of the crank which is supposed to fling the oil back into a "gutter" which leads to a passage back to the sump. At the back of the block what's critical is the clearance of the seal plate,held on with three screws, and the rear main cap where it opposes this same area, and the crank. You can adjust the position of the plate for minimal clearance. The bearing cap, however, is what controls the clearance of the bottom half of the equation. If the crank flange(the "flinger") the seal plate, or the bearing area is damaged you'll probably have a leak. I use a strip of paper to establish the seal plate clearance. Remember that the rear bearing should actually be "glued" into place to prevent leakage past the sealing areas. This is an excellent place for Hylomar, as it retains its lubricious qualities as you tighten down the bearing cap. If it's any consolation, no matter how careful you are, some leak....some don't... Just be careful not to overfill the sump.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon