My father started selling lubricants in the 30's. I am 67 years old and still sell lubricants. I have been to lots classes and and seminars over the years. I am careful not recommend brands I sell. I do not sell Mobil, but I think they have a good answer to the question. http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/GL-5_and_GL-4_Gear_Oil.aspx