IMO, anyone who might replace a steering box just because it has "play" in it is wasting their money. It seems to me that MB has built in an adjustment to the steering component and one should make the adjustment when the steering becomes loose.
At about $300-400 a pop for a new/rebuilt box, this could get mighty expensive...especially if you have more than one of these MB creatures.

My 300D has more than 278,000 miles on it and it still has the original steering box. However, the SL only has about 95,000 and I recently replaced that steering box. Why one has lasted so long and the other so much less is a mystery to me, but that's the case. I also replaced the coupling on the SL at the same time the box was replaced.

For anyone replacing their steering box, I highly recommend Performance Products as the source of the replacement.

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Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000