when a geartrain is brand new it will shed the most amount of debris in the first 20,000 kms. MB make really really nice n smooth diffys and fill them with nice oil too - which honestly is overfilled IMO (just like everything on the car, e.g. double the regular quantity of engine oil to a massive starting battery)
A good idea is to change the oil anytime it gets mixed with water or gets some dirt in it or burns out from overheating (mismatched tires left to right, breather damaged etc). Under good conditions I have seen and serviced a bunch of these cars and the original fill was pretty dark n dirty, MB specify a regular (but heavily dosed) gear oil for their open diffys and after a change - you can inspect it after 50,000 kms - it will be shiny as the day you put it in.
I personally use a nice synthetic blend gear lube in the USA, In Pakistan I bought Mobil1 gear oil from Mobil Askari lubes. You can choose to buy it from Mercedes Benz (at a price) - but make sure that you are choosing the right oil (sometimes the guys at shahnawaz ltd are also lost in their heads)
Its a very long specced oil. dont overdo it though.
addendum - MB do specify a synthetic lube in frigid areas or extreme hot areas (desert) and on some high end cars to quieten gear noise.