The B-O-P seal is available from Spotts, Pontiac Dude and many others. It is the best. One more thing to make sure about: The PCV valve MUST be working for the seal to be effective, otherwise the pressure in the crankcase will push oil past the seal.
Helpful tip: When sizing the seal PER THE INSTRUCTIONS (right-o, Steve) use the rear cap to hold it while you file it. This will make perfect sense while you're doing it.
