Bonding agent for a thru-hull depth finder transducer (probe)

For several years the hull mounted transducer beneath the engine stayed securely in place and worked fine. Last season it popped free from the "glue" holding it in place. I do not know what agent the dealer had used for the install, but it had the grey appearance of JB Weld and held well for over 18 years. The several bonding agents I tried since then hold poorly and the transducer usually breaks free within a few trips on the lake, apparently in part due to the vibrations and slight flexing of the hull, but mostly due to the poor bonding. And I did clean and lightly sand the mounting surfaces.

What bonding agent (brand and formula nomenclature) has worked well for you, and will not interfere with the signal that has to pass thru this glue? Appreciate all suggestions as I am at end of ideas. I am about ready to just forget about the depth finder!

Thank you for all replies.

Sounds like a "thru the hull" application. Any good epoxy (without any fillers) should work well. We used to use marinetex at the boat shop for that job. The trick is to make sure you get the active portion of the transducer sitting in a good puddle so no air pocket is created. You may also use some laquer thinner to wipe things down, after sanding, before you apply the adhesive.

Appreciate the reply. After getting no replies for over a week I went ahead and mounted the transducer with 5200 then went on vacation till now, so I just now saw your reply. I haven't used the boat since returning so do not know if the transducer will signal thru the 5200. Have carb apart today so it will be Monday before I know.
Thanks again for the reply