If it is the same as the one I am thinking of, my mechanic used to take another key for the same lock type, put it in and give it a descent smack with a hammer. He said it would pretty much fuse them together. This is easy in a marina when there are spare keys hanging around, but you could always buy a new one.

ive cut off 23 locks this year at the shop due to people buying boats and not knowing locks were on props or where keys were..air cutter with cut off wheel taking off outer sleeve,then air chisel to break off then air chiesel with sharpened pint to help spin off lock nut ,just dont hit threads good luck

I meant if someone wanted to take them.

Thanks proboat Wes. I'll give the air chisel a try. You're right on, just bought an old Velocity with Bravo drive and no prop key for lock.