I'd left home in my 2000 M5 w/ 46k miles (out of warranty 3/2004) and while driving, heard some fan squeal. Wonder what that's about? About 4-5 miles later at my stop, I exited my vehicle and noticed a slight smell. I hadn't been pushing the car hard or anything but it smelled a bit like, well, oil on manifolds.
After my visit, I returned and started driving back down the lane I was on. Hmm...there's a narrow black stripe on the street I didn't recall on the way in. Was I just not looking? My wife starts wondering what the heck I am doing as I start veering right to left on the road while watching my rear view mirror. A second black stripe is following my course! Uh oh. Temp gauge...reading ok. No oil light. Engine sounds ok. Hmm... Pull immediately to side. Walk to front of car...look under car. It is bleeding a pricey Castrol death. Pop hood...Gadzooks!
Towed to dealer. Oil coming out of Vanos solenoid gasket, need to replace Vanos unit (both replaced a few years back under warranty). Hey!?!?...if it's just a solenoid gasket, why not just replace it? Even the first mechanic suggested doing that (about 1/10th the cost), and they don't even have to remove Vanos. Only after digging did it become clear that the solenoid gasket is not supposed to have to battle high pressure oil and that the piston seal in the vanos unit failed allowing the oil to escape to parts not designed to deal with it necessitating vanos removal/replacement (& new belts/cleanup). Fortunately, I caught the problem early and still had oil in the crankcase but I could just as easily have melted the motor.
I looked around and saw some old posts on Vanos and oil leak, but nothing too much lately. I'm not expecting advice or pointers unless someone has some secret BMW handshake that uncorks an extended warranty I wasn't aware of. I'm just providing a data point if someone else encounters this. I'm not happy since at about twice this repair I could get a new Hyundai or somesuch but I am just figuring my turn was up.