I'm betting on a washer fluid leak, mine has a sleight drip and when the fluid is topped off, it leaks a little bit in the same location you described. BMW OE fluid is a light blue color, not at all slimy or oily, and no particular smell. It really doesn't bother me, but i'll have it looked at next time im at the dealership.
E88 N54 Alpinweiss/Coral Red/Motiv HTA 3586r Tial .82AR/Other stuff...652WHP
F30 N55 XDrive EBII