In most cases, just install a new key. But, if there are grooves in the flywheel or shaft, get some 'valve lapping compound", apply a small amount, assemble without the key, tighten the nut so the flywheel will still spin. Apply, tighten and spin, repeat, till everything is "lapped" in with each other. Clean everything, including the threads, install the key, assemble, and torque.
Thanks for the replies. We got the right offer for this one so off it went. We gave the buyer the spare bottom end, so there is everything needed if he wants to swap out crank.
Hated to let it go, but I needed the garage space to ramp up for snow season. Plow truck, salter and 4 blowers eat up space, but thats what pays for these toys!