the problem like the one described is almost always caused by the owner of the boat .
the most wide spread problem for the keels on these swing keel boats is caused when the boat is moored for a long period of time and the owner cranks the keel up as its moored....
this allows the keel to rock on its pivot bolt and the hole to wear in the direction of "escape", or towards the edge. AND, the keel WILL rock more and farther side to side when its cranked up than it will when its down, locked or not... the keel is designed to be stable when its down with the lock bolt in place with the tension removed from the cable. it IS NOT designed to be stable at at other position or configuration.
also, if the lock bolt IS in place, you have collectively more surfaces to wear, so it will take even longer to wear a noticeable amount.
its perfectly fine to moor the boat with the keel in the down position, as it has a lot of wearing to do in this position before there is any chance of the hole wearing thru....AND it will take longer to to wear any given amount, as the motion is reduced considerably.
It should never be moored for any length of time with the keel up, as can be seen by the wear, and the direction of wear, on the pivot hole.
with normal usage and overnighters, weekends and such, with the keel up will NEVER be a problem for many, many years with never a thing to worry or wonder about, but the long term moorage with a retracted keel will eventually become someones problem
when the hole wears directly toward the edge of the keel, its not because the boat has seen a lot of use, but because it was moored with the keel up.
salt water will allow it to wear more quickly as there is a higher corrosion factor, but even if the keel were in the down position without the lock bolt in place the hole could wear a couple of inches without worry of escape.... with the lock bolt in place it will add extra support and keep it from EVER becoming a problem in our lifetime....