Back when bikes didn't have gauges, using the odometer was the only game in town. Now that even the cheapest bikes and cars come with a gauge, I think it's time to insist that the gauges actually work. And it's not that difficult, even the cheapo cars on the market come with pretty accurate gauges these days. There is no valid excuse for a Harley gauge to be less accurate.
btw, using the odometer works fine if you always remember to reset the odometer at each gas fill, and of course you always fill to the exact same level in the tank, and of course you always ride under the exact same conditions so that you use fuel at the same rate. Seems a little shaky to me, versus a device that should tell you how much fuel remains regardless of all those factors.
To answer the OP's original question, yes the gauge can be fixed. If you have a really good dealer, it shouldn't be a problem. If you have a typical dealer, you may have to escalate things above them or do it yourself.
Jerry