IF it is the steeringdamper, it is cheap ( @ 30.00 ) and easy to replace.
Two bolts/nuts to remove and it's done.
To test it, you could undo 1 end and push/pull on the free end, to test for resistance.
If it extends/collapses without much resistance, it is shot.
Here you go.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1XC0ZKQX91YF1DUCFL&year=1991&make=MB&model=300-E-002&category=M&part=Steering+Damper