The float is sticking, probably due to buildup on the strut or wires that it runs along as the tank fills/empties. You can remove the guage from the top of the tank and carefully open the tube to access the wires and float. I used a large pipe wrench to take off the collar. The tube is opened by a small nut at the bottom of the guage. You have to be very careful taking it apart, the wires themselves are very thin and can easily break. Once apart, with care clean the middle pole that the float runs on. Don't try to clean the wires, they will break if you touch them, guarenteed. If all goes according, you should be able to get it back to working. If you should break a wire they can be replaced. I was able to source the sending wire as 42 guage nichrome wire, iirc. The second wire is just for the warning light and is regular fine wire. Good luck