Just what I needed. :(
Unfortunately I didn't notice the puddle until about 2 hours after I parked so any traces of the liquid on in the engine compartment are long since dried up. I am off work tomorrow, so will be checking it out. The drip spot appeared to be fairly far back, so I'm hoping it's not the headgasket leaking (which would be the third in as many 535is, dammit).
Any tips on how to find this are appreciated, I'd rather not have to get the car hot and then crawl under it. There are so many coolant hoses around that back of the motor I'm hoping it's one of those.