I did a lot of research on trucks before I bought my 2008 Duramax. As I recall, one problem many of the early 6.4l Fords had at the time was diesel diluting the oil in the crankcase supposedly due to fuel getting past the rings during a regen of the DPF. Check how long it has been since the last oil change and pull the dipstick and see if it looks overfull. That was one of the signs. One user reported when they went for an oil change the oil came out with the viscosity of water. I haven't followed up since I made my purchase so I'm not sure what fix Ford came out with. That said, with 108,000 on the clock and still running strong, this vehicle may not have that issue.