I had a problem with my 500 box leaking and desided to reseal it.
I found a site with great instructions that also included the adjustment.
How to reseal a MB steering gear
The instructions start with "remove the steering box" which I don't think you want to do just to adjust it but maybe you can get an idea of what needs to happen when you adjust it.
I followed all the procedures and every thing turned out great.
Sitting still, it feels like it has some play in it but I determined it was in the tires and very little in the box. The steering box has about 226K miles on it. It came out of an 89 420SEL back about 10 years ago.
Paul