If Sierra makes one I'd try that. What I found on the Cobra units is that the shaft that turns the potentiometer gets sticky and sticks in one position, a little bit of back and forth movement and lubrication with Boeshield or similar and it works fine again. Before condeming the one you have get someone to watch the dash gauge while you move it through its travel.
The funny thing is I was going through my spare parts bin (when you have an OMC you always have a collection of spare parts because you can't just go out and buy many items) I found an OE sending unit I bought and never used, because the Sierra unit as lasted so long.
