My 1991 126 suffered leaks, and was easily repaired with a seal kit.
But a few years later the car developed instability in winds, and the tension adjustment seemed to do nothing for it.
I decided to try a rebuilt box.
What I got for my $325 appeared to be an old box for a 1982 240D. It was the "correct" part number, and would bolt in; but it had no wear compensator (my '91 does), the digression valve was wrong (don't know what effect that would have), the actual steering ratio was wrong, and the tension/drag was not adjusted at all.
It was just an older box not really built fo a 126, that apparantly had just been re-sealed and sprayed with a quick coat of paint.

Sent it back, took my box out, partially dismantled it, and did a very careful tension adjustment. I fabricated a little arm to hang weights on, read and interpreted the book, and tweaked the exact on-center drag.

Seemed to work well, no play now, feels like new.
Only special tool was a postage scale to weigh the sockets I hung on the bar for the correct tension weight.

So, my advice would be to work on the one you have; send it to Larry and let him tweak it, or try it yourself if you have the time and the manual, and the understanding of ft-lbs vs newton-meters and all thay fun.

Cheers,
S-Class