I know the ml430 uses 75w-90 or 85w-90 gear oil but I would like to know if it's ok to use 80w-90 gear oil in both differentials.

 

You can roll the dice and see, but there is a reason for everything.

 

I bought the 85w-90 for all 3 of my transfer cases. My mechanic used a synthetic he prefers instead. I believe there is chatter out on the forum as to this subject.

 

My ml has high mileage and I've never changed the diff oil or the transfer case oil, and I've noticed my ml rolls downhill very slow, almost grimy or sluggish until I tap on the gas and let it roll, then it goes rolls downhill smoothly with out any gas. So I know its a must to change the fluids, I have 80w-90 laying around and just wanted to know if the viscosity is good enough to run in my differentials.