The clue of "really feeling it in the floor" is your best bet. Check out Fastlane, suspension, and guide rod mount kit: http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1MH0N4O9B1NO0L0CHA&year=1984&make=MB&model=300-SD-002&category=L&part=Guide+Rod+Mount+Kit These are mounted in the suspension bearing brackets http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1MH0N4O9B1NO0L0CHA&year=1984&make=MB&model=300-SD-002&category=L&part=Suspension+Brng+Brkt which are at your feet. Probably one of the first suspension wear items on the front end of a W126.

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Sam

84 300SD 350K+ miles ( Blue Belle )