It's the front control arms. My '87 300DT has the same symptoms and was checked by an expert on these chassis. He aslo suggested replacing the rear control arms as they play a big part in overall control in cornering.
Do you also feel a little instability when coming into a dip at high speeds? The steering will tend to drift slightly to one side when going over a bump (unloaded) if the front control arms are worn.
Around $210 per side and its not an easy job.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!