Rebuilt my buddy's motor 1959 18hp. He had used it twice. Worked great. Then took it out last weekend and he was trying to back troll and his motor would poop out of R and jump into N. But worked just fine from N to F. His srew that goes into the chuck dog broke on the out side. Just the head of the screw. I asked him not to run it before I fix it and he used it anyway.... now he has that problem. Any help thanks