The cone had a bit of the inside of it broken off. My theory is that maybe this imbalance caused the cone to wobble
No absolutely not.
The prop nut should be tightened to the correct torque. This pulls the prop onto the shaft and if it has been done correctly, the nut should be able to be removed and you should not be able to pull the prop off with out a smack with a hammer. The safety
system is the Nut and the set screw. There simply is no way either can come out with a wobble of the nose cone. The nut is there for the one reason of ensuring the prop does not come lose due to improper gear
changing, like that clunk when put into gear
when the engine
still has too many revs on it. That is not the best for things. The set screw is the "Lock" for the prop nut. The two can or should not be able to simply come loose. Even with a vibration of the nose cone.
The issues will be....The anti-seize applied to the shaft has stopped the prop pulling up properly onto the shaft. The prop has worked it's way on over a long period of time while the engine
is in gear and the prop pushing hard onto the shaft. Therefore the nut will now be loose and the set screw may possibly also become loose. Not sure how, but obviously it has.
Sean, the drawing only shows the splined shaft, but I assume the tapered the shaft also has a keyway, is that correct??