More than likely the head or front timing chain gasket need replacement. The M103 and M104 engine are well known for their head gasket issues. Depending on how much oil you are losing, you can delay the repair of the head gasket, providing oil is not entering the coolant and you watch the oil level closely. Eventually, however, you will have no other choice but to get the gasket(s) replaced. Have you pinpointed the exact location of the leak?