there has been two kinds of Sonic Speed sensors used by AMEL. The first ones (until around 1995) were glassed in the hull/keel stub and impossible to replace without digging and re-glassing.
The second type called "en ligne" which means "lined up", is installed in a GRP tube glassed in the hull/keel stub, including two O-rings.
You have the second type. I called POCHON (the electronics supplier for AMEL for more than 30years) today and they have a pair available.
You may get in touch with Stephane at stephane at pochon dot com.