I second the recommendation of Dextron III. I have owned Mercedes for the past 12 years and used this tranny fluid. It's listed in the owner's manual.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member