they make plastic melting tips for soldering irons,that would work better than sealer.it looks like it leaking at the copper post that goes thru the plastic. sealing from the outside doesn't work as good as from the inside but unless you have a large access on top you are out of luck.you could seal the whole thing and just put in another sensor. it looks like the sensor is less than a dollar but the tool to put it in is $127.00.
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