check your engine mounts... there should be 13mm of clearance between the bottom of the metal shield and the front crossmember.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1FX0MB1RS1HV15UR4Y&year=1991&make=MB&model=300-CE-002&category=A&part=Engine+Mount
There are 2... drivers side is easier to check... passenger side is harder to get to.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/showpost.php?p=831799&postcount=13
http://www.peachparts.com/shopforum/showpost.php?p=831807&postcount=14