I have been using the M1 5w-40 for a little over a thousand miles now. I checked it today and the oil is still honey colored. The car runs smoother than before and just keeps getting better. I have noticed no sluggishness from it at all. I took out the Castrol the dealer put in by mistake because I had my own oil to use but they did not look in the trunk to get it. They use semi-synth 10w-30 at the dealership when it says in my manual that 40 wt's are to be used and synthetic at that. I have M1 10w-30 in my truck and have no complaints about Mobils products for German cars.