I just replaced my shaft after finding it eaten about halfway through. My prop was fine. Someone else on here had a boat with about as much time in the water
between haulouts as mine and his prop was eaten, but his shaft was good. It was suggested that if the current
is from inside the boat, the shaft will be attacked and if the current
is from the water
the prop will be attacked. Personally, I don't understand why there would be a difference.