Well, to wrap up the wiper problem, here's the epilogue.
As you recall, I was driving along and lost the gauges, wipers, and the transmission went into limp mode. An automatic circuit breaker was cycling under the dash - trying to repower everything but finding a dead short to ground it would immediately trip again.
I troubleshot it to the wiper motor shorting internally. A new one is very expensive. I was gifted a whole wiper motor assembly that worked, and slaved it in to check my troubleshooting. The wiper motor spun the shaft without causing the short circuit. Although free, the mounting stud was wrung off:
This is what it's supposed to look like:
I attempted to make one from the two I had - bad motor good stud & good motor bad stud, but that wasn't going to happen.
The stud is a 1/4-20 course so I went to home depot and picked up a tap in that size. My intention was to drill the shaft as deep as I dared to, thread it, and epoxy a bolt of that size in the hole, then just cut the head off to the right length.
I should have gone with a smaller size bolt, as the shaft's flats, that engage the wiper linkage, don't leave much room for error. My benchtop drill press was all I had to work with, and getting the hole perfectly centered and perfectly straight was mostly successful. Mostly...
I actually broke thru on one side of the flat a little, but I don't think that stud carries much load, it just keeps the linkage from wandering away from the motor shaft.
Here's the result:
Mostly straight, and epoxied into the hole. Once the epoxy cured I used a hammer to coax it into straightness so it was square to the shaft axis as best I could get it, then cut the head off.
Installing it in the truck was fun, in the dark, but I got it installed and I thought I had indexed it correctly but...
The sweep was perfect, clearing the windshield like they're supposed to, but they were parking on the wrong side. I have just enough OCD that while it worked great, it wasn't right.
Back out this afternoon and pulled the motor back off, manually dragged the wipers over to the proper park position on the right side of the glass, and reinstalled the motor.
Everything is back to normal. I'm hoping it all stays together long enough for me to find a good used one.