Please take a look at the attached picture I've just drawn, and you will see why filling up the differential unit with gear oil when your MB car's rear is lifted up is actually better than filling it up when the car is at horizontal level.
Gear oil lubricates the differential innards by the splash method, and it has very powerful anti-foaming additives to counter the oil foaming due to splashing, so overfilling a differential unit is OK (actually it's good IMHO). However, what I'm talking about only applies for MB cars, because overfilling final drive units on some other car models (some Ford ones) is actually bad.
Be sure to use only gear oil with API GL5 75W-90 or 80W-90 on your Mercedes cars. 80W-140 is too thick and should only be used in racing cars, SUVs or trucks. Differential units on most MB cars accommodate about 1.1 - 1.4 quarts, depending on models.