My hood tach needle seems to stick around the 1500 rpm mark. I'm not sure if it's an original or not. It's accurate after that but doesn't drop down to zero after car shuts off or below 1500 while running. I know I can have it reconditioned but am saving that for the last resort. Is something sticking (perhaps oily residue)? It was working correctly at one time. Can I fix it myself? Any help/info would be greatly appreciated. Thanks.