Not to be too picky or anything, but you should not be using an acid based flux for wires or electronics in general.
What sensor is that? And did you assemble the probe end your self or get it ready made? I put some ds18b20 sensors on the ends of 3.5mm jack stereo cables, into 316 stainless caps (from home brewing supply places) and filled them up with epoxy. As a strain relief and a little extra water proofing i put glue coated shrink tubes over half the cap and onto the wire a good inch or so. Came out like this:
