on my 1998 C230 the FUEL GAUGE SENDER UNITS are located in the fuel tank.

located at the lower front of each half of the fuel tank. have to work on them when tank is empty and battery negative cable dissconnected.

and I think you need some special tools to do the work

get parts from FASTLANE, link at top of page on this site.

there are sensors, but I don't know enough about incorreect gauge readings to know what route to go.