OK here is the new one for the day. First some history on the 84 300SD. Box has been adjusted, all front end joints inspected and several replaced, steering damper new, new shocks. In all my reading it appears that I have done (or have had done) all of the factors that affect steering play. Its not huge but annoying, the movement the steering wheel must go through before the wheels turn. In my reading it in fact may be within "normal" range (1 inch at the wheel) but I am sure it is at the far end of normal.
Best left for pros?
Can be done by any good mechanic with tools?
Buffoons like me? (I did do water pump on my own!)
Have a great day

So,

Are you asking about replacing it or adjusting it some more?

Not too bad of a job, if you've done tie rods and other parts swapping out the P/S box is just a few more bolts. I would maybe try and tighten it up a bit more, just for grins, before I dropped the bucks on another one. There is a procedure for doing this, wheels must be straight ahead, some sort of alignment pin in the box specially designed for this but I have never used it. Remember, counterclockwise on the center adjustment stud will tighten the box. Test drive it and be sure it does not stick right or left, it should self-center itself somewhat.

I am sure there are more experienced folks here that may chime in soon.

BTW, I know where you are coming from, I had an 79 450SL that suffered from the same problem. Car was just plain squirrelly, didn't matter what I did, could never get it totally tightened up and ended up selling it for partially that exact reason.

Adjustments have not solved the issue. They seem to make the end point of this "movement" more harsh, so I think its on to a new box, and probably , the more I read, one that is best left for the pros.
Thanks 126