Just one man's opinion.

If you are using The Right Stuff between the upper pan and the block I'd bet that is the source of the problem. RTV is too thick and creates a gap between the two parts that is preventing the rear main seal from sealing against the crank. I cross referenced Loctite 574 to Permatex 51813, bought it at my local Napa, and it worked wonderfully. The specs say it is designed to fill gaps up to .015 (Anaerobic Gasket Makers & Flange Sealants : Permatex® Anaerobic Gasket Maker) so you can see it is designed for much tighter assemblies than an elastomeric gasket maker.

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'82 300D - Light Ivory, 2nd Owner (Back in the wind April 2013!)

'95 E300D - White, grey interior. (Suffering from stuck/broken glow plugs)

Deuteronomy 22:4-
"Thou shalt not see thy brother's ass or his ox fall down by the way, and hide thyself from them: thou shalt surely help him to lift them up again."