I've never cocked a main seal in over thirty years of building Mopar V8 BB or SB Most rear main seal leaks are in the side seals or at the mating surfaces of the oil pan gasket on the rear main cap on the SB
Do NOT put any silicone between the main cap and block That will add clearance between them allowing oil pressure to push it out
I do apply a tiny thin retaining layer of silicone sealer to the back side of the main seals, both on the top and bottom
Good luck on yours