Although I'm not certain what brand Superformance uses, they are probably the same Viton rear seal that the Fel-Pro is... they are all sourced from major "seal" manufacturers. Changing the retainer is most helpful.... regardless of the seal source.

I'm a former long-time aftermarket engineer from Fel-Pro.

Mopar Mitch "Road racers and autocrossers go in deeper and come out harder!"... and rain never stops us from having fun with our cars... in fact, it makes us better drivers! Check out MOPAR ACTION MAGAZINE, August 2006 issue for feature article and specs on my autocross T/A!