Hello,
I have seen in the web that what happened to me has happened to many others. I refer to the gearbox dipstick (Yanmar part number 177070-62450) that brakes as depicted in this picture.
I made a piece with a M18 x 1,5 nut and an aluminium tube. But in the end I fixed the original piece with 4 small screws.
In the Sea Knots Beneteau 40/43 forum I learn that there is a site that sells replacements in aluminium.
Regards, Luis