I've built and raced a bunch of stroker motors with no knurling on the main seal surface with no leaks using the new type of Viton or neoprene rear crank seals
I had more troubles with rear main seal leaks on BB using the old rope seals
That knurling provides a small shallow path for oil to leaf out of
I've had that surface polished a lot by crank grinders when having stock cranks ground down on the rods and main journals to help seal the rear mains up
I also use a good brand of adhesive silicone to completely seal the side seals up on the rear main seal holder and the block