I'm sure you know that MB steering boxes adjust backwards from the rest of the world.
Turn the adjusting screw "out" to tighten the gear mesh inside. Be careful, though. A little bit goes a long way and too much is said to damage things.
My personal technique for finding steering play is to have a kid turn the wheel back & forth while hold my hand over each of the components. The loose one kind of jumps out at you that way. The steering damper has nothing to do with play, it just damps oscillations.