I was asking this same question last winter, in the end, I used a Fel-pro seal, # BS 40245. Probably the equivalent to your Viton. Summit Racing carries rope seals, someone gave me the number back then, it was for a GM, maybe a Buick. I don't know if I can find the number. I did what I was told to do by Mike at B3 Racing and my oil leak is gone. Seems like I explained all of this awhile back, wasn't it you?