I had the box on my 300D rebuilt by a local indy when I first got it. There was at least 2 inches of free play and it was a PITA to drive on the highway. As I recall, it cost me about $200. I don't how many people rebuilt these things. It's probably easier to just buy a reman unit:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ41QD0LJAFD&year=1977&make=MB&model=240-D-002&category=All&part=Steering+Gearbox