That backs up some of the arguments in here that the service department is using the bulk oil versus what the manual recommends. The semi-synthetic is their bulk stock. May not be much of an issue between semi-synth and full on synth, but then again what's the difference between a Chevrolet and a Cadillac?I've had dealer (free) oil changes since new. I asked the mechanic what they use. 5-20 synthetic blend. 40,000 + miles and counting.......