My guage also went after 2 years, just replaced it, tehn took the old guage off, ripped it appart, "reset" it by bending the mechanism inside it until the needle dropped to ) but did not bottom out completely on teh stopper peg.
After this i figured - "yeah right McGyver, I highly doubt this thing will work again". Unscrewed the new (now 15 minutes old) guage, put the old one back in, and voila, EXACTLY the same reading as the new guage gave me seconds earlier.
So, now i have 2 guages that are OK, if one goes, I switch to the other and fix the uncalibrated guage using my new McGyver calibration technique.