2006 Audi A4, 3.2L V6 FSI, 6 speed manual transmission. 50/50 city/highway driving. 15 mile commute to/from work each way, with stop and go traffic in the afternoon.
Oil changes with Castrol Syntec 5w-40 were performed at 5K, 10K, 15K, 25K, 30K, 35K, and 40K. Switched to M1 0w-40 at 48K, and...