Have a look under your car, when it gets warmer outside.
That's why there are " left " & " right " fuelsenders.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1XC0ZKQX91Z40QB4GV&year=2000&make=MB&model=C-230-002&category=E&part=Fuel+Level+Sending+Unit
The " reserve " is part of the whole system.
This is what the tank looks like:
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=202085&M=111%2E975&GA=722%2E605&GM=717%2E460&CT=&cat=45H&SID=47&SGR=015&SGN=01

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2007 C 230 Sport.