I am in process of solving a similar problem with my 530i. Oil pan has been wet for 2-3 months but source is not obvious from below. Try looking under the valve cover on the block to see if there is any obvious signs of leakage. You can do this from the engine bay with a flashlight. In particular, look at the engine block behind the oil filter housing and under the intake manifold. This will definitely require a flashlight. My problem is at least partially due to a failing CCV system that must have been cracked and was leaking oil onto the block. I may also have an oil filter housing gasket leak but no way to tell yet. The CCV on my car failed big time ~10 days ago and I was suddenly burning tons of oil. I replaced the CCV and all hoses this week and found the engine block behind the oil filter housing and underneath the intake manifold was covered in oil. I also found the power steering hoses are leaking and contributing to what is dripping from my car. The best way to inspect these is to drop the plastic cover underneath the engine. My car has about 130K miles on it.
Last edited by mda185; 02-10-2013 at 06:38 PM.