Maybe you are refering to the fuel injector holder O-rings?
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1HJ1DL3DD1K81DI4S7&year=1991&make=MB&model=300-CE-002&category=C&part=Fuel+Inj+Holder+O-Ring
They would go around the injector holders http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1HJ1DL3DD1K81DI4S7&year=1991&make=MB&model=300-CE-002&category=C&part=Fuel+Injector+Holder
that can stay in place when changing injectors and seals.
Bruno

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1992 300TE 160 kmiles