Steering wheel slop (again)

Greetings,

I recently adjusted the steering box on my 1970 220 (W115) and unlike the previous posts I've read, there was only one nut (other than myself) which was 17mm. The bolt takes a flat-head (yuck) instead of an Allen wrench, and to take out the play, you need to turn the bolt clock-wise.

Well, I didn't take the steering box apart so I don't know how this adjustment takes the play out. My questions are: Is there a danger of over-tightening the bolt? Will it cause increased wear inside the steering box if it's too tight?

I've checked all the linkages and they seem fine. However, I assume there will be a point where adjusting this bolt will have no more effect and I'll have to replace the entire steering box. Is this correct?

Thanks,
Skrunch.