Have you run a compression test on the engine? If you ran a compression test and found two cylinders low, squirt a little oil into those cylinders, turn the engine over a few times, and run the test again. If the compression is higher now, the problem is rings. If it is still low, the problem could be valves, or it could be a leaking head gasket. In either case the fix will be easier if the compression is still low after putting in the oil.