I had this problem just before xmas. The valve cover gasket failed. Once I had fixed the valve cover gasket (I did both even though only one had failed), I went to work on the vent hoses and oil separator.

I have the V8 engine. I'm not familiar with the inline 6.

You can tell right away if you've got 'moisture laden' oil buildup by pulling off the two crankcase vent hoses from the top of the oil separator. If you look in the hoses and the entrances into the oil separator and see some creamy gunk stuck to the walls of the tube then you've found it. Another tell tale sign is finding this creamy white gunk under the oil fill cap.

I removed the vent hoses and replaced them. I also removed the oil separator and the short hose that is attached to the bottom of the oil separator. Both were full of the condensation. I cleaned them out by running hot water and dish soap through them until there was no more gunk coming out. I re-installed them. It took a lot of trial and error because you have to reach behind the engine and make sure the hose gets set back on the oil return pipe. You can't see it when you are installing it. Check www.realoem.com for graphics showing the oil separator, bottom hose, and oil return pipe.

I hope this helps. The fact that this is a problem is my only big disappointment with the X5.