windshield wiper transmission
 

I noticed the wiper on the driver's side of my 1995 S420 does not have the same same windshield coverage it used to. The wiper arm does not seem to reach out as as far as it sweeps the window. Could the wiper transmission have failed?

If so how complicated is the replacement?

According to this: http://63.89.49.212/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1R510G7PR1RH1C9O5M&year=1995&make=MB&model=S-420-001&category=P&part=Wiper+Blade
there is quite a bit of difference in length between drivers & passenger side.
Does that have anything to do with it ?

Your wiper transmission has probably failed, it has a feature that extends and retracts the blade as to wipe the top left corner.
It's a 1400 part
It's a fairly common problem and many have found it to be a gear that breaks inside the tranmission. A few have had a new gear made and put it in with success. I've tried but couldn't get the transmission apart, i drive with it broken now. No big deal.