Dude, I think the same exact thing has just happened to me. I found a decent amount of fluid (which was not oil) under the middle of the car. I haven't done anything to the car (lately), so I'm a little unsure. The other part that confused me was that I always see transmission fluid as reddish in color. This was light brown like new oil, but thinner. Have an appt with BMW on Monday...so we'll see.
13 535i Msport