2003 Mercedes Benz 500

IN JUNE 2012 THE CAR DID NOT PASS INSPECTION AND WE WERE TOLD WE NEEDED A NEW GAS CAP. WE GOT A GAS CAP AND IT PASSED INSPECTION. SINCE THEN WE HAVE HAD A STRONG FUEL SMELL WHEN THE GAS TANK IS FILLED COMPLETELY. IF WE ONLY FILL THE GAS TANK ABOUT 3/4 OR LESS, THERE IS NO GAS SMELL. WE RECENTLY HAD THE CAR SERVICED AND THE MECHANIC TOLD US THE GAS CAP NEEDED TO BE REPLACED AND A SEAL/CAP IN AN OVERFILL TANK UNDER THE REAR SEAT WAS LOOSE. WE REPLACED THE GAS CAP AGAIN AND THE CAP TO THE OVERFILL TANK WAS TIGHTENED. WE FILLED THE TANK FULL AND HAVE A VERY STRONG SMELL OF GAS SO THOSE REPAIRS DID NOT FIX THE PROBLEM. IN A REVIEW OF SOME INTERNET RESEARCH, WE SAW THAT NHTSA AND MERCEDES-BENZ WERE JOINTLY INVESTIGATING A FUEL LEAKAGE IN THE UPPER PART OF THE GAS TANK FOR E-CLASS MERCEDES PRODUCED BETWEEN 2003 - 2008. WE THINK WE HAVE ONE OF THOSE FUEL LEAKS. WE WANT TO SELL THE CAR BECAUSE WE HAVE PURCHASED ANOTHER VEHICLE BUT DO NOT WANT TO SELL IT UNTIL WE HAVE FIXED THIS FUEL PROBLEM. *TR