I have just done it on my clk a208 which has the 722.6 gearbox.Got the atf from mercedes think it was atf 154.
When i went to do mine it was a bit of a pain, the sump drain plug had been well damaged.
I thought no problem going to drop the sump will drain it there. Wrong one bolt useless abd one snapped off when went to undo it.
I would but new bolts from mercedes when u do it they dont cost much, plus the genuine fitler and seal.I got 11 litres of atf and just had enough. You get about 4 lts from sump no diff drain plug on mine so u need to put what ever comes out back. Then follow the pipe from the gearbox on drivers side to the union, need 17mm and 19mn spanner to undo.
Start engine and run 3lts out into bucket then put 3 lts new back in. Do this until it runs out nice clean red, took me 3 times