Guys, I would be suprised if this "sensor" can determine with accuracy small viscosity differences, 5w20 or 0w20 or even perhaps 5w30 would be much more difficult to determine than the outside temperature which many of our cars can't even do (mine is ok now with v3.61). Think about it, as simple a device as a thermometer is and it's not accurate why should this viscosity sensor be any more accurate. Lwood, what does your dealer charge for a synthetic oil change? I agree with you fully on synthetic, the cost difference of the oil is laughable, I showed months ago in another post the difference over 100K miles is less than $300 (6K intervals). Other than not getting what you wanted and paid for, I would'nt worry too much about M1 vs Syntec, the metal alloys in your cylinders will appreciate the fact that synthetic is in there regardless of who makes it (as long as it's a full synthetic). It still vexes you though if you are an M1 guy to have a brand in there you don't want. Wal -Mart has 5qt Jugs of M1 for $19.86, you might pick up a few and bring it to the dealer (you should'nt have to, but if you want it done right...) and of course a discount for not using thier oil.