This happened to my friend's Cape Dory 25 and it was a strange problem.
A thru-hull had been installed but the outer sealant was compromised
and water got at the edges of the hole. Inside it was still watertight,
but the glass actually was weakened. This may or may not be the case
with the Beneteau, which had did have a problem in the last decade with
a bad lott of thruhulls.
Luckily all of my thruhulls were replaced in late 2004.

Sorry, gents!

RB
35s5
NY