I have the 2023 HD All Weather and the owner's manual recommends 80W-90 GL-5 for all drivetrain components. I have read a lot from other posts about how GL-4 is the recommendation for previous model years so not sure why the change? I doubt they changed much in the drivetrain except differential gears. I realize some of the manufacturers say their product works for both specifications so but am mainly curious why Mahindra changed the recommendations for the newer models if the drivetrain is largely the same. I'll probably go with the GL-5 oil per their specifications but please let me know if I should use GL-4 instead.