Before you replace your motor, have someone look at it. Your problem could be as simple as a brush stuck or worn down. If the motor is damaged, you can probably find someone to rebuild it. I understand that it is a truck starting motor, but start with the brushes. I know this because it happened to me. Place a tarp under the boom when you take the cover off. If it is like mine, there is a lot of carbon dust in there.
With luck and cooperating officialdom, I will be in Newport, RI by the end of June.