After you eliminate the steering links and ends for play, take a good look at the rubber flex joint that is just above the steering box, inline with the steering shaft.

Also try to make and adjustment on your steering box.
It is true that the steering boxes wear rather quickly in relation to the rest of the vehicle. However one thing I have encountered is that we have the tendancy to subconciously compare steering to cars made in the last ten years.. The technology is different and make very noticible changes when comparing them.

Measure the actual play at the steering wheel for how much play you really have.

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79 240D my current toy
42 years a Diesel addict

240D sold
250SE sold
220D sold
280C sold
280S sold
300D (2) sold
300CD sold
300DT sold
300SD sold
380SL sold