I don't know what can/might happen inside the steering box if over tightened, but I did experience a similar situation on an old pick-up. After replacing the king pins and tie rods I adjusted the steering box to get rid of the last bit of slop. I over tightened the adjustment screw, and for the life of me I could not hold that truck straight. Seemed like even the heart beat through my fingertips affected where the wheels pointed. It was as if driving under the influence of many beers and trying to hold a straight line.
I backed off the adjustment just a little, so there was about 1/2 inch play in the steering wheel and all was well. The secret is having someone inside the car working the wheel side to side as the slack is removed. Show them how much slack you want, and when the steering wheel moves only that amount, you're good to go. Not sure if this method will work on MB's, but it might.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.