If I were you, I'd make a point of keeping the keyway filled with grease and the tumblers flooded with lubricant (not necessarily in that order...)

I have a stainless hitch pin with the same type cylinder lock that is unworkable due to salt getting in and freezing everything up. Will need to cut it off when I need to remove it.

jky

Thanks. i usually do, this was old wear and tear from previous owners. In the end i ditched the hitch as the breaking mechanism was stuffed too, so i removed all the breaking gubins as the boat is under 750kg so not needed. The rest of the cables hubs etc were all going to need replacing anyway.