I have seen a broken chainplate on a Beneteau
"Oceanis 311". The boat was built around 1998 and the breakage occured in 2007 after intensive sailing with a cruising association.
In fact, the part was made by Wichard, of round stock, bend in a U shape with both ends threaded to accept hex nuts under the deck
. The breakage on both ends was under deck level, in an area not accessible for inspection
without removing the part.
The breakage might have been caused by anaerobic corrosion
but, as far as I know, the association owning the boat obtained no explanation from Beneteau