Charlie, I have two E320 cabriolets and a 300CE but fortunately haven't had a fuel gage issue yet. I have heard that fuel pump sending units at least for the coupes have become unattainable. Several thoughts for you:
- put in an ebay search for these and patiently wait for results
- pull the sending unit and read the resistance values as the float is manipulated; I would suspect some bad areas on the wires that make the circuit. Manipulation of the float up and down its travel may clear this up.
Beware of a couple of things:
- I would do this with the tank almost empty, working around gas is still hazardous
- I have had the aluminum cylinder around the sending unit drop off into the tank (and it's still in the tank) - the loose cylinder was the source of the problem.
- It's a good idea to have a new tank seal available as you don't want a leak here.
Good luck!
Gary