Now that I remember, I believe my '83 300D has a W116 steering box in it. It has a '85 300TD differential I know for certain. For a short time it had a steering wheel out of a W126 that was not the right seat, it used the same spline but instead of a cone seat it had a flat seat for a big nut to hold it down. It looked odd too as I recall.
Anyhow find a tight steering box off a low mileage car (not a W115) and you will be a lucky man!
Changing this is a PITA as far as I am concerned.
DDH

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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!