Not much to my surprise, my hack-job thermistor rebuild went bad:
Having nothing to lose, I heated the brass tube over a butane flame to wreck the epoxy, which blew out with a satisfactory bang and filled the Basement Laboratory with The Big Stink.
Much to my surprise, the active ingredient still worked:
The multimeter reported absolutely no intermittent dropouts for as long as I was willing to watch the trace while doing other things:
So it must be my crappy soldering technique.
A brace of real M2 thermistors will arrive shortly …