I have almost completed my restoration, the tractor starts, runs & drives. Until today. It seemed as thought the engine was seized at first, starter would not turn it. I had to manually turn the engine with a strap wrench to loosen it up. with persistence, I was finally able to get it started. Once it was warm, it started no problem. After it cooled, same problem. Any Ideas? Clutch disengaged, oil full, starter ok.