I only use the Fel-Pro Vito rear main seals, part number 2947 and cost $25-$30.

Taken from 440Source "They have a much greater resistance to high temperatures than standard rubber. It also doesn't have a tendency to dry out and shrink over time."

I also do not use the side seals, I use black RTV, either Permatex Ultra Black or Right Stuff. I clean the surfaces, fill in the sides and then installed the seal and then fill in the back cavity with RTV.