Fuel gauge problem

i have a 2001 range rover 4.6 hse and the fuel gauge always says full with the reserve light on. i went to a few different range rover mechanics and heard different answers from each one. The best solution i received was to change the gauge inside the dash which is held in with 2 screws i was wondering if this is possible and the best solution instead of having to get a whole new dash causing the mileage to be different.