I don't know when it was last serviced and i don't know the type of oil they used when it was serviced.
what type of engine oil do i use for my ML MERCEDES BENZ 320? on 2001 Mercedes-Benz ML320
Don't you have an owners manual?
synthetic oil 5/w about 7-8 quarts mobile only
mobil one is the best but pricey the grade should be on your oil fill cap