Posting this in case it might help somebody else. After a track day on Saturday, I noticed that I had a belly pan full of oil, and I was down a quart. I figured it was probably a loose oil filter (even though I ALWAYS torque mine to spec), but I looked at the Sharpie marks I made when I tightened the oil filter, and it hadn't moved. Odd. Must be something else... I cleaned up the oil and kept looking for where the leak was coming from. It wasn't until I actually started the car and then got back underneath that I realized the oil was coming from somewhere above the flat, round oil plug (see the first pic below). I traced the leak up to the engine oil pressure sensor... Bingo! The factory witness mark showed that the sensor has backed off a quarter turn, causing the leak. (See the second picture below.) The good news is this should be a simple warranty item ( I just hit 2 years & 8,000 miles), and it will be easy to keep an eye on in the future, since you can see the sensor when you remove the driver's side front wheel. So, be sure to check your engine oil pressure sensor before your next time out on track.