Although our car, a 2013 BMW 740 Li Xd only had 18K miles when we bought it in July 2016 (it now has 51K) the idea of changing the differential oil at 60K miles (and 80K on the Transmission) did not particularly grab my attention as BMW did not recommend having it done...at all! But because Tom at Automotive Excellence recommended having it done nonetheless, certainly made me think twice about the notion because I trust his person; his knowledge, and experience in automobiles. (His shop also does the repair on our 92 Saab 9000-Turbo as well). So today, despite still having 10K more miles to go I decided to go ahead and have the differential oils changed, and a good thing I listened for the oil was black meaning its viscosity has diminished considerably and is no longer optimally protecting the gears. What a sigh of relief to know that the car is once again in exceptionally good condition and I'm glad I listened. Thank you Tom for giving the advice! And Thank you too, Angela! Stay Safe! Oni Sioson East Haven