It is not the seal itself, nor the seal surface on the Crank... been there done this a hundred times.
Listen closely.... if you want to cure the rear main leak, once and for all !
The problem;
The groove in the Block, that holds the upper half of the rear seal, were NOT machined at the same time as the Mains on BB Mopars, and are NOT concentric with the mains.
If you look closely with the Crank and upper seal half installed flush with the parting line in the Block, you will see that one side will be compressed with the seal lip "tight" and sealing on the Crank..... and the other(offending) side barely touching.
This is a very common problem on BB Mopars and should be checked/ corrected on assembly.
The cure;
Offset the Seal installation about 1/4" to 3/8" above the parting line on the "offending" non-contacting side.... so that it fits UP into the Seal retainer as it is lowered into place.... then use a small screwdriver to move the retainer OVER as it is installed.... dragging the offending seal side into contact with the Crank.
Obviously here, the retainer side fibre pieces are deleted to allow the retainer side-to-side movement. Clean well with brake clean afterward and just silicon up the retainer from the outside.
Tip;
usually a good idea..... to also have your guy machine about .010" off the retainer on his Connecting Rod Cap Cutter first, before installation. This provides a little added Seal compression against the Crank.
There has been about 40.... Billet, shiney, start trek, 007, wiz-bang type Seal retainers offered in the aftermarket for BB Mopars....NONE cure the PROBLEM.... because the retainer is NOT the PROBLEM !.
It is the groove offset in the Block !
So install the seal offset above the parting line on one side..... (AFTER you first mock-up with it installed flush to determine which side the seal is loose on), then use the Seal Retainer as it is installed, to drag the Seal over into Crank contact.
Bob @ rmp Race Engines