OK,then, if it was mine, I'd drive it. Worst thing could foul the plug once in a while, so carry a spare. By changing oil often, you will clean out any crud thats in the motor. My guess would be valve seals. You wouldn't have good power and compression with bad rings. I was thinking maybe a stuck pressure relief valve on the oil pump, but I don't think so. I had an AC 500 (Suzuki) with a stuck relief valve, it ran really high oil pressure, but never had a leak or a problem in 9,000 miles. I don't think changing out valve seals is a big job. Maybe you can find a youtube video.