I decided to post a quick follow-up to the original fix I'd implemented about ten months ago.
The $1M question was...
How Long Will a Silpat Keep The Misbehaving Thermistor In Order?
My low-budget fix worked exceptionally well for far longer than I'd expected, to be quite honest. I'd been able to print a bunch of stuff for MMS MOA way back in May, and then my printer had a pretty extended dormant period between early May and mid-August when I started designing some other projects and things.
I'd actually had replacement thermistors on hand since the beginning, but the idea of tearing things apart to replace it was just not high on the list — especially when I had a functional workaround. I also wanted to thread the replacement (and the ribbon for the BLTouch leveler) through the cable loom from the motherboard to the hotend and that all felt like a lot of work.
It Started Happening Again
I noticed that I could go about a week or so with frequent printing before I needed to give the thermistor screw a little tightening. It's a pain to adjust due to tearing apart the hotend assembly, so the pain was getting to be an issue. I didn't look closely but I figured the silpat was finally reaching the end of its second life, deteriorating, and becoming the cause of the screw consistently backing out.
But I was on a production schedule of sorts, and taking the time to dig into it before MMS Miami was not in the cards, especially considering I had the theatrical show preparations and run the weekend before. So I kept it rolling the "fix" way, but by the time I left for Miami I was adjusting the screw every other day.
Tear It Down and Do It Right
I took an hour or so and tore down the printer, extracting the thermistor and stringing a new one through the wire loom along with the BLTouch ribbon, getting everything tidied up along the way. The rebuild wasn't especially exciting, but it looks a lot nicer and tidier than it did beforehand.
However, as I expected, when I pulled the silpat chunks and failing thermistor from the hotend, the silpat bits quite literally broke apart between my fingers. It was nearly toast...and had really deteriorated in the months (and many hours) of being directly exposed to 200°C temperatures.
So the answer to the aforementioned question is
About Six Months of Frequent Printing, Max
I'm glad I did the little experiment, and it was definitely a moment of "I can beat this thing!" I don't have a lot of hours on the replacement thermistor in its normal/traditional/correct configuration, but thus far it's been running swimmingly!