OK,,, I have been through this hell before.
I had my 383 engine built by the best in the business; a professional, 30 year, race engine shop.
First run it leaked on the stand. Second seal...leaked on the stand.
We pulled it apart 4 times.
We checked and sent the crank out to an expert. Perfect crank.

Finally...
He tore the engine down to the bare block. Checked everything with a micrometer. After measuring and researching we found that a small percentage of MOPAR block rear main seal retaining threads are drilled off to one side, ever so slightly. It is literately thousands of an inch off. Enough for a small leak according to Felpro.

He eventually used an OEM rear main seal retainer (they have some slop in the side to side placement. Driver to passenger side movement). He shimmed the retainer to one side the distance it needed to go to center the retainer exactly over the crank and to pull the weak side seal over to the crank surface. If you look closely you will see the weak seal side against the crank. also you will need to have the seal slightly off center in the block and retainer to have the retainer grab and pull the weak side over to the crank as you push the retainer to one side.

This is about component machine errors. DO NOT believe in crap like the type of knurling on the crank end, Rope seal fixes, and other non-mathematical crap. It's all about tolerances and measurements. Something has to be measurably wrong. either the crank is off or the retainer/block is off.
Don't grind the retainer to make it tighter. Look at the seal as it presses all the way around the crank. I believe he said he used a snap gauge to measure the exact distance it was off from center and that measurement is what he used to push the retainer over.

My engine builder now checks every MOPAR block for this error. He spent months on my engine and cost him time and money that he does not want to go through again.

It was a nightmare. I feel your pain. My engine is now dry and runs strong.