I hear your pain, my son and I just finished putting a new milodon pan and windage tray on our 440. Ours leaked at the rear and my worst fear was the rear seal too!

Crank flange was dry, so was flex plate and converter.
This is the third pan, because of damage when removing the others for different reasons, tray too.

On the plastic tray; we thought 'great idea', not so much for us, leaked a lot at the rear and I think it was because they were designed for a pan with flat rails, not like the standard MOPAR pans withe the stiffening dimples.
Maybe they are designed differently now, this was a few years back...

Also tried Andy F's pan rail flanges with a new dimpled pan, this also didn't work out as the flanges are best used with pans NOT dimpled.
I think with some modifications to the design they can be effective, though.

We usually use Hi-Tack on just about all our gaskets, both the spray and brush type with excellent results.

This time I noticed a slight difference in the height of the rear seal housing versus the block's pan rail so I filled that gap with "The Right Stuff" then used "Hi-Tack" on the rest of the sealing surfaces.

As I noted in another post, the Milodon windage tray needs some cutting to fit over a standard pickup, probably designed for theirs.
Not hard, just overlayed old tray and marked the difference.

Haven't put oil in yet, sorting out some other problems, I used to tighten by feel too, this time I set per MOP's 200 inch#s I was surprise how much tighter they were versus "Feel".

Good luck...Joe

PS the two pan bolt holes into the rear seal housing on ours were "open" holes, I used some sealant on those.