As David pointed out, overfilled transmission could certainly cause spilling - in fact some transmissions have a valve to release excess pressure when the tranmission is hot - idealy this is for air but if fluid level is too high it will of course come out, too. In fact if this valve is blocked it could cause excessive pressive inside the transmission casing resulting in leaks somewhere. But I do not know whether your transmission has this valve.
I suggest you go to a MB dealer to pull out what on the car had been repaired/replaced under warranty to have a better idea as a whole as well as whether your car has undergone any tranmission work before. If affirmative, fluid overfill cannot be ruled out.
Does your car have the 5 speed transmisson which has the life-time fluid and the mechanic-only dip stick? May be you could ask your mechanic to check out the fluid level and where the leak is from.
Good luck and keep us post.