You have a smoking BMW due to bad valve stem seals. The valve stem seal problem is that the old valve stem seal becomes hard over time and doesn't provide the proper seal between the seal and stem. This allows oil to pass through and enter the combustion chamber and exhaust. The oil consumption here is bad for a lot of different reasons. Obviously smoking, but also decreased catalytic converter life. We've seen a number of cars that have set CAT inefficiency codes and these codes can go away if you replace the seals if done in time.