Thanks so much for your (quite divergent) views!! The pitting (at least where it is deepest, up to 1.75mm, and can become an insurance problem) seems to be only along the waterline. I guess over-plating this or treat otherwise isn't that expensive? Also the seller says they would pay for it but I wonder if the problem is then solved or just postponed. Interestingly, the survey from around 3 years ago which detected the pitting problems around the waterline didn't propose to take any measures.