Hello, first timer. Have '97 Cadillac DeVille with 80,364 miles. Taking oil consumption test and dipstick currently indicating one section above add. Have used premium fuel until recently when on advice of experienced service tech,changed to mid-grade. Believe that premium may have been causing carbon buildup in piston rings causing them to stick and using more oil than it should. With mid-grade carbon buildup could be dissipating due to a faster burning fuel than premium and therefore burning off that carbon. Any opinions or suggestions? Thanks very much.