The final email from BMW Tech Support stated that some oil in the air intake of the diesel was normal, that the sensor was faulty and the car should be returned to me. I know turbos need oil to lubricate the bearings and this diagnosis seems strange but I did read the emails relating to my problems and that is what the local dealer was told by PUMA which I understand is worldwide BMW Tech Support. As I said earlier I have not noticed excessive oil usage of any type so we will see if the problem is fixed.