The 2017 ST Supplemental documentation specifies a replacement oil that meets WSS-M2C913-C spec. Unfortunately it does not appear that Mobil (US) makes a current fully synthetic oil that meets this spec. Seeing as my 17 is at its' first oil change interval, I want to make sure that I don't void its' warranty or cause an issue. I prefer to use mobil fully synthetic oils in my vehicles. Figured I'd see what you guys are doing for your cars.