Since I plan on changing the oil in my 2.8 12 Audi soon, and because I'm not going to use M1 0W-40 again, I decided to just get some GC and top off with that. Now, quite frankly, I rarely believe in any hype, and I'm not favoring any oil under XW-40. So I dumped a bit over 1/2 quart of GC in, and the motor sounds better. I asked my girlfriend if she noticed anything, and she said it sounded quieter (I hadn't told her what I'd done). I don't think both of us are imagining this. If 1/2 quart of GC on top of 4.7 quarts of M1 makes a noticeable improvement, then I must wonder if GC is really the Holy Grail of off-the-shelf oil.