Rip off. That's a little under 4 hours of labor around here which is nuts. Changing the transmission fluid in a Mercedes is no different than any other car really. They suck it out and pump it in, and change the filter. They probably won't even drain the torque converter. Take it to a local MB mechanic and supply your own fluid if you are paranoid... or not if you don't mind spending a lot of money on routine maintenance on an old car. Better yet do it yourself on the street.

A tranny fluid change every 20K miles seems excessive to me.. what does your manual say.

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1985 CA 300D Turbo , 213K mi