Looks quite familiar to me.

It's one off the notorious places of a cat where the stainless steel meets aluminium with a little devastating electrical current as result.

Problem with repair is that maybe the whole surrounding of the bolt-hole in the beam is affected. I didn't hear you talking about this; maybe it is not visible.

And yes you maybe can solve this by a big washer, but I would have doubts. By the way, the old Prindles had an aluminium strip inside the beam where the the two bolts for the dolphin-striker where fixed. So you had to replace the strip as well.

I suggest you to de-mount the forebeam anyway and inspect everything carefully.

I remember also that the old nacra's with the round beams broke a lot on this point because of these problems with usage on saltsea.