My Indy told me that the adjustment of a W 124 steering box should be performed at the workbench so I am not certain that it could be done on the car. Even worse : in any of my documention is there a mension of an adjustment.
He told me also that MB prescribes the replacement of the steering box on a W 124 every 300000 km !?!?
Mine, with the front wheels straight ahead, hasn't any play after 326000 km so I am not to worried about it .