I believe mine is a K72B. I have always used John Deere Hygard low vis, since that's what Deere calls for. I have read a couple posts from people who have used Mobil 1 synthetic in a Tuff Torq, particularly Mobil 1 Extended Performance 15W40. I have had excellent luck with M1 in my vehicles, and am curious about how it would work in a transaxle. Does anyone use M1 in this application?