Got rid of the bubble, stood it perfectly upright in the freezer for a few hours and it (bubble) was gone. DId some searching on-line and found out it is a fairly common problem,(separation, they call it) several websites advise tapping the bulb, smacking it gently in the palm of your hand, or swinging it abrupty. None of those techniques worked though... I even stood the bulb on the chocolate vibrator for a minute, but that didn't work either. Standing it upright in the freezer worked.
The thermometers from Matfer aren't cheap, and are quite large (aprox 9" tall) and robust, I have the s/s 'cage" that slides over it, so I'm not ready to toss it out just yet. At the moment, I haven't found a "bricks and mortar" store that stocks these thermometers, and I live in a fairly large town. I know I can get replacements from Matfer or places like Chefrubber, but I'd have to put in an order of at least $150.00 to make it worthwhile to pay for shipping charges.