This is the part I replaced on mine:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ428E134D19&year=1983&make=MB&model=300-DT-001&category=All&part=Ignition+Switch