This applies to S500 and S430 models from 2000-2006. A big shout-out to member rob_fed of the benzworld.org internet forum for the fix which he had applied to his 2006 S430 back in November of 2012. This video is pretty much a depiction of his description as reproduced below:
“Finally took off my driver’s side visor…
a. Lubricated the rotating shaft with a teflon based light oil I used on RC cars
b. After working the shaft extended and retracted the smoothness came back with rotating the visor up/down
c. This did not fix the visor from sagging
But this did….
With the visor off, the shaft will rotate 360 degrees in ether direction. You can feel the detent of the up position and it clicks or notches in firmly as it sets. The detent is what holds the visor up in combination of the “sticktion” of the rotating assembly.
When remounting the visor, I could feel the smoothness when everything was lubricated, but when pushing the visor all the way up, the detent as missing. I took the visor off and rotated it again and the detent was fine. What gives??? Somehow, I assume with wear, the position or clocking of the detent moves from the original position. Only by a couple of degrees. When I remounted the visor, I put a couple of washers under the mounting point farthest from the windshield. This puts a slight angle on the mounting point and allows the detent to catch.”