they are called buffers, mercedes number 615-988-00-11 you will need 3 see link below for purchasing them or your local dealer.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?header=header.jsp&footer=&product=615-988-00-11&partner=mercedesshop&baseurl=http://catalog.peachparts.com/&clientid=catalog.mercedesshop&cookieid=1TZ1CPY8T1TZ1D76XF