I own two MB's and love them. Also owned tranny shop for many years.

If the fluid smells burnt (burnt "toast") and looks that bad, sorry its ready for a rebuild.

We would had refused to change the tranny fluid as it would further the problem and strip the clutches as new fluid is very "detergent"

Also sorry to say Mercedes makes a poor tranny (ZF's) and they just don't hold up as others.

John1