Well, thanks to Stlhotrod's sage advice I was able to replace the R's engine coolant temperature sensor weather pack connector. As mentioned earlier the brittle retaining clip snapped off when I pulled the wires to change the #1 spark plug.
The new connector and removal tools arrived yesterday so I set aside some time to watch a couple of DIY videos, threw the fender cover on and dove in. As Stlhotrod said, it's fairly straight forward, although as with a lot (most?) of the engine work, space is a big challenge. Fortunately the sensor is fairly high up and, well, not terrible to reach.
After a few attempts at inserting the correct terminal removal tool into the connector and tugging on the wires, nothing would budge. Inspecting the new connector I found that the end that fits into the sensor itself can be removed. That would give me clear access to the tiny tabs that hold the terminals in place. So I popped the same piece off of the existing connector. There they were... and they were just as hard and brittle as the retaining clip. I tried raising them and tugging on the wires again but no-go. I pushed each tab up a bit more and "snap" what a happy sound (this time). With the tabs out of the way the wires slipped out easily. So in the end I didn't even need the speciality tools, but I have them JIC there's a next time.
I took photos of the two-wire orientation. 50/50 chance that it could be wrong, but with me, it's a 100% chance that it would be.
So I swapped out one wire at a time to be certain. Once they slid in place I replaced the end piece and it looked like new. A few more contortions and it fit back into the sensor with a satisfying "click" of the retainer clip.
Fired her up, ran it for a bit and it all looks good... no errors and the temp gauge appears to be working fine. Phew!
Not the most fun thing to spend an hour or so on, but a good learning experience. I've attached a few photos (in addition to the ones in my original post) showing the various stages of R&R.
Thanks so much Stlhotrod! You're a life saver!