I changed transmission fluid and filter in a 98 ML320 yesterday. The following observations and comments might help other members who are thinking about doing the job. Overall, it's an easy job. If you can change oil in your car, you can do this job.
The truck has 56,150 miles on it. The driver is conservative. The fluid was coffee color. I don't know if the brown color is from deterioration due to operating conditions in the 722.6 tranny or because the red dye in the fluid is unstable. There have been enough comments in this and other forums about 722.6 transmission failures to make me believe that "sealed for life" means until the transmission dies, not for the life of the car or truck. The smart money seems to be on changing the fluid and filter instead of running the old fluid to the point of transmission failure.
I drained 3.7 liters from the oil pan (including residual fluid which won't drain from the screw plug) and 3.7L from the torque converter. Eight (8) L will handle your refill needs.
Not all the fluid will drain from the oil pan because the weld nut that the plug screws into is pretty thick. Bring the oil pan down level or you will have a mess on your garage floor. Or maybe on you.
You might want to get a large piece of cardboard from a refrigerator box or mattress box and put it on the floor before driving the vehicle into the garage. When the job is over, just roll up the cardboard and throw the spilled transoil away. Sure does make the cleanup easier.
The filter is held in place by the pan. There are no attaching screws. To remove the filter from the valve body, pull straight down. To install the new filter, lubricate the o-ring on the filter neck and press into place. There is a tab on the filter top surface which fits into a slot in the valve body. Use new seal rings on the drain plugs. The seal ring part no is 007603 010100.
I made a dip stick from a length of plastic-covered Bowdin cable from a dead lawn mower. I used a triple-square file and made notches in the plastic cover for full-hot and add-hot. The full-hot level is 65 mm from the tip. The add mark is 54 mm from the tip. A conventional metal tape-type dip stick won't work. The fill tube has bends in too many directions. MB has put out a bulletin advising its techs to ensure that the transmission is filled all the way to the full-hot mark and not short of it.