Have you checked the oil fill port cap for being fully sealed? I lost the O-ring on my Kohler once, and it decided to blow oil everywhere. It has been a while, and I really don't remember the exact details, but the O-ring either got damaged or fell out when I was checking the level 'out there' instead of in the garage. It made a surprising mess.
tom
ADDED: If you actually have high pressure in the crankcase, either you have an air leak or the rings are allowing too much blowby. The former is the pumping action pulling air through a leak, and pushing(trying anyway) to push it back out as the piston comes back down. Blowby is the engine itself providing excess air into the crankcase, where it goes through the same process.
You could get a plastic bag or grocery plastic bag, rubber band it to the dipstick/fill port, and run the engine. If you are pumping air, the bag should blow up even though it is sealed, indicating air supply from elsewhere...
tom
