[SpeedBuggy]

Try a search on the following, all known issues.............
*Broken valve cover or head bolts which were a common mode failure. (Leak may be noticeable under engine, oil residue on side(s) of engine block)
*Oil Filter Housing Gasket Leak, (Leak may be noticeable under engine, oil residue around oil filter housing)
*Mechatronics Sealing Sleeve, common on 3 series with ZF Transmission (used on 330i) (Leak may be noticeable under transmission, passenger side and /or oily residue on transmission)

My Mechatronics seal leaked on my 330i after the car sat for almost a week, had a puddle about the size of a baseball on my floor. I would suspect this over the oil leak.

Use the search feature above and search the forums (not Google), lots of posts regarding all above and may help to determine what you may be experiencing.