M1 has high mileage 5W-30, 10W-30 and 10W-40.
Originally Posted by bluesubie
If you aren't having leaks then you may not need to switch. The Mobil1 HM oils have additional seal conditioners, have a thicker viscosity within the same grade, have a higher High Temp High Shear, and have more anti-wear additives when compared to the regular oils. There is an M1 5W-30 High Mileage oil. Some people run them just because they're more robust.