I have an issue with the speedometer on my '69 bird. The miles do not turn anymore and the speedometer works randomly every time in a while for a short moment. But even when it works the miles do not turn. What do you think guys, should I take it off and try to find and fix the failure or go straight away for a new aftermarket one? What could be the quicker checks I could perform to see if any easy fix could be possible? Thx