Anyway, after some short diagnosis, I determined it really was the caliper, not a bad hose, sticking slides, or sticking parking brake cable. Bad caliper. I had Carlota order some loaded calipers for the back.
OK, no go. We'll get Semi Loaded. After much waiting, and bad communication, the calipers sat in the store for a week before they would tell her, not that she didn't poke them about it.

Turns out the semi-loaded DO NOT come with the bracket as advertised. They do come with the caliper bushings. They also come with 3 out of 6 hardware clips, two of which are somewhat unecessary.

Anyway, I did the left side:

I finally found the proper sanding discs which i like to use to make the rotors nice... at a paint supply store. Pretty shiny, eh?
The sanding discs sold specifically for rotor refinishing just aren't up to my standards, esp for a rotor darkened due to sticking brakes.
You may say "why not replace the rotor or have it turned?" Because there is no need. Check your factory service manual. These discs have <.003" runout, <.0003" parallel variation, and <.020" scoring. Turning removes metal, making the rotors thinner, and introduces runout when done on a bench lathe. Plus this car is on the cheap for the Grassroots Race ;)
Not to mention the pounds of dough saved in labor by not having to R&R the rotor on this model.

Anyway, I went to put the old caliper core back in the box for returning, and found the real culprit causing the piston to stick:

The dust boot was torn, allowing the piston to corrode and stick. In light of this, I decided to replace the other caliper ONLY if it could be determined that the replacement would be better. I got to use my handy-dandy rear caliper kaboodle
(I couldn't buy it seperately from the kit)
to push the piston back in.
The right side piston went in smoothly. The dust boot is not torn. The bushings and clips are in acceptable shape. Now lets hold the brakes on and make sure the stress of pushing the piston back in didn't compromise this delicate hydraulic component.
Hooray! All good. That'll save a mint.

Here's a picture of the left side brake pads versus the right. When i checked them only a month or so ago, they were all about the same. Now you can see the left side is down almost to metal, and the right side is only about 1/2 or so worn. That boot has probably been torn since 2 brakejobs ago, and the piston just now came out to the point of where the majority of the corrosion on the piston was... just a guess.

Anyway, I think we'll return the caliper purchased for the right side. The new parts were kind of a dissapointment anyway. At least the caliper works correctly out of the box (sometimes they don't).