I've always wondered about the .01-.02mm spec. The spec for my '63 Corvette and '76 Cosworth Vega is .001-.005" based on a 20 thread per inch spindle, a six point castle nut, and two pependicular cotter pin holes, which varies the clearance about .004" with each twelveth turn of the spindle nut. The front wheel bearing setups are basically the same, but the Mercedes allows you to achieve an exact clearance with the pinch nut.
On my vintage GM cars I've found that shaving the washer to achieve clearance in the range of .001-.002" makes the steering feel more precice.
These tapered roller bearing designs must operate with slight clearance or they will fail, but Mercedes spec of .00039-.00078" seems to be cutting it too fine. Could it be that the .01-.02mm spec is a misprint and it should really be .1-.2mm. The .01-.02mm spec is in my 1984 introduction manual. Is this consistent with other Mercedes service publications?
Trying to read half a thou with a typical dial indicator setup (as shown in the photo) is iffy at best. I've checked/adjusted the front wheel bearing clearance on my '88 190E by snugging the nut until I could not feel any play while wiggling the assembly by grabing the top and bottom of the tire and then backing off the nut until I could just feel a tiny amount of play. It's almost something you can "hear" more than "feel". The RH side was okay. The LH required a bit of snugging. The spindle shoulder that the inside bearing inner race rides on takes the cornering load, so it can wear slightly in many thousands of miles, which will tend to loosen the clearance a bit.