After hearing about, and seeing several boats, with problems at the attachment between the main boom and the mainsheet, I went back and took an extra careful look at this part on Harmonie. No evidence of any problem (or any repair) at all. Having gone looking because I was thinking this was a weak point in the design of the boom, and coming into our boat after it has already completed two circumnavigations, I was fully expecting to find at least a subtle issue I have missed before.
NOT finding it had me wondering: Why? What could cause a failure of this part, other than normal time and wear?
I am pretty sure I have said this before, but... there are two important things to remember. First, of course, is to use your preventer whenever possible. It would be nice to say "always" but sometimes you just have a little way to go, and it is a bit of a pain to rig, so...
The second point, and I think even more critical, is to use the traveler.
If the traveler is centered, and the boom is eased using only the sheet, it can gain great speed and momentum when it gybes. The force required to stop it can cause damage in a number of places, and the attachment point of the sheet to the boom is obviously vulnerable. If the traveler is dropped all the way down to the leeward side before easing the mainsheet, even if (when!) a gybe happens the boom crosses only about to the center line, and the force needed to stop it is greatly reduced, along with the potential for damage.
I know both previous owners of Harmonie were very fussy about using the traveler. With over 100K miles under her keel, I imagine she has seen more accidental gybes than I have inflicted on her, but with the traveler always down, it isn't nearly as hard on the boat as it might otherwise have been.
I have seen some really ugly things happen as the result of accidental gybes on non-Amel boats. From broken blocks, through broken booms, right on up to dismastings. Anything that can be done to reduce the forces involved is a good thing.