Got a motor from my dad. Serial #4713924. Best I can tell, the newest it could be is 1977. The story is that the crankshaft splines are stripped. He was told that was the issue over the phone by an old boat mechanic. Now that may be the case, but I want to be sure. His issue was that the prop will spin at low rpm, but slips when you give it gas. I'll try to attach pics. I really don't know much about the guts of a boat motor. When you turn the prop by hand, it makes kind of a clicking noise and the long skinny shaft runs through the lower unit doesn't move. Should it?