Pirelli Peeler

I had the same thing happen to me today when I reversed into a parking space I got a big waft of blue from the tail pipes & I gave it a rev and also got blue. When I started her up again 15 mins later there was no sign of blue and hasn't been since. I too have a decat pipe, on a scorpion exhaust. My oil is still showing full. Perhaps the oil build up you're describing is just burned off every so often & the lack of cat makes it more obvious. Doubt it's rings, you'd need to over heat the engine for them to buckle, then they wouldn't seal & it would constantly burn oil.