Drive shaft splines

[Carl]

As I mentioned in another post, my motor failed in a big way a few months ago. I have ignored it as a coping tool the rest of the fall since I did not fish since the end of September. Anyway, the motor has run flawlessly all year and even the day it failed. After hours of fishing and repositioning, I went to move and started the engine and shifted forward and the motor revved really high like the engine was not in gear, but it was. I lifted the engine and checked that nothing was caught, fouled. Everything seemed fine, but the same thing happened. I thought I spun a prop and had to call for a tow home - good thing I have a tow service contract. A few days later, I dropped the lower unit and found the splines on the drive shaft had hard burnt metal between each spline. I looked up at the mating splines on the crankshaft and found a smooth surface. There are no splines on the crank. Some folks at work have said I must have hit something, which I did not. There was no warning to this. Also I drained the lower unit oil thinking the gear box is trashed, but everything seems to be ok. The oil was clean and the prop spins with no noise or grinding.

Has anyone heard of this happening? Is it worth fixing or are there most likely other things that are now overstressed due to the type of failure. I found a place that can rebuild the engine, but I am not sure it is worth it.

What do you guys think? Any / all comments appreciated

It is a 1988 Mariner 150 HP

Thanks

Carl