I had the same problem with my '02 325i. Valve cover gasket went one morning. Ashes actually started coming through my vents from the oil burning as it leaked out. Had the valve cover gasket changed at a nearby shop for $200.
One week later, oil still leaking from the valve cover gasket. Brought my car to Endras BMW. Paid close to $1000 to have the crankcase vent valve replaced. Expensive repair, but no more oild leaking onto my engine