Use a ATF oil with the newest MB specification for the 722.6 tranny, which is 236.14.
http://bevo.mercedes-benz.com/d/d/en/Spec_231_1.pdf

Change also the ATF oil filter - that is important.
Level the ATF oil correctly. That's very important. If the oil level is too high, or too low, the transmisson won't work smooth. Both can harm the transmission.