Help! Crankshaft Woodruff Keyway
 

I had a mechanic replace my radiator - all good. But now the harmonic balancer pulley won't stay tight. Now, I suspect I'll have to replace the woodruff key and maybe even the balancer itself. I had to drive it about five miles home after the steering went out and I discovered the problem, so there's probably some damage there. So, if the keyway was damaged, how does a mechanic fix that?