[quote=sr4440]

I can tell you that stock style BBM rear seal leaks air bad under a vacuum. The front does also but not as much. My 512 B-1, it had 6 inches at idle and 12 during a pull with lots of oil pouring into the vacuum pump. (a dyno pull takes longer then I am under power at the track). Knowing I had air going by the rear seal, I changed it out to a double lip design, went to 11 inches at idle and 17 during the pull and NO oil.
Joe
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Joe do you have a part number for this seal. Darren, AL do yo run your rear main seal installed backwards? If so does it seep at all?
Doug