The best way to attack the problem is to determine if you think this is a problem with the compression rings or the oil control rings. If you’re looking at cleaning up the compression rings, I would recommend trying Berryman B-12 Chemtool Total Fuel System Cleanup (part #2616), which is our strongest detergent-based fuel additive.  This product is available on Amazon right now for $13. If you need to clean up the oil control rings, I would put 1½-2 fl oz of Berryman B-12 Chemtool Fuel Injector Cleaner (part #0116) per quart of oil capacity into the crankcase when the engine cold.  If your engine holds 6 quarts of oil, you would introduce 9-12 fl oz of 0116 into the crankcase.  Then, run the engine for about 10 minutes at idle and check the oil to see if you need to change the oil and filter.