I'm a little surprised at how dirty the oil looks. Is this a carbureted engine? Maybe the upside down ring idea is not so unlikely, or maybe the fuel/air mix is rich enough to be contaminating oil, or maybe a little of both.
I've never tried it, but I don't think it would be hard to push 15psi past the intake guides. Could you tell where it was "leaking"?
I can't remember the OP, and am too lazy to look it up, did you do a leak down on this engine?
