Thanks kurb. Of course you are right, there is no way tightening the bolts would have stopped that leak. However, something has to have caused the damage to that gasket. I can't recall seeing a gasket damaged in that way except by it adhering to a bolt when the bolt was removed, so the damage may have occurred when you dismantled it. Nevertheless, when you open the crankcase in a case like that, it is good practice to push a 1/16" drill bit through the PCV oil return passage, circled in green below:
[Linked Image]

Just hold the drill bit in your fingers, and do not rotate it, or it will catch in the mesh that separates the liquid oil from the droplets, inside the PCV compartment.

The problem you are having putting the hub back over the Woodruff key, is the converse of the good luck you had when you took it apart, in finding that the key was not tight in the keyway. I suggest you take the key out of the keyway in the shaft, and try to slide the top of it into the keyway in the hub, starting at the end of the hub that goes onto the crankshaft first. If it won't push in under firm finger pressure, you need to look closely for a burr or dirt in the keyway, or some minor damage to the top of the key. Also check that the keyway in the shaft is clean, and the key will fit into it right to the bottom.

Remember, the key has to finish up being a good fit in both halves of the keyway (both crankshaft and hub), or it will knock annoyingly, and soon wear out. Do not file down the key, but if you find a nick or burr, you can smooth it across with sandpaper.