I had this procedure done seven times before BMW finally agreed to replace my 1998 Z3. The fuel sending unit is located behind your passenger seat. there is a cut out in the carpet to permit access to the unit, which you probably didn't notice until the dealership failed to put it back neatly. ANYWAY, I spoke to a regional representative from BMW USA about my concerns regarding the repeated failure of this unit. He informed me that the fuel sending units in ALL Z3's are defective in that the gold plated connections used in the sending unit are prone to corrosion, especially in the northeast where there is a higher sulfer content in gasoline. This inevitably leads to the gas gauge fluctuating between full and empty when the tank is completely full. Accordingly, many Z3's will require this part to be replaced periodically, ie every 6000 to 30000 miles (mine was every 6,000). BMW has been working on a replacement for this part for quite sometime but has yet to be able to design an effective replacement. For some reason, BMW has left most dealerships in the dark about the nature of the problem.