Okay, following up with pictures/disassembly steps. Similar "one slider wouldn't power-unlock" problem to OP; installed a junkyard door that also does the same exact thing. Hopefully it's a coincidence, the motors are my problem, and not the computer not spinning it for long enough or something.
The lockbox/latch assembly is held into the door with 3x T30 screws by the latch. The door card/trim pops off, you pull out the manual lock toggle on the inside of the door, and the box falls down. Remove the inner and outer door handle cables and undo the trim clips along the wiring. The box looks like this:
You need to pry the sides away from the "top" at the top and bottom of my photo to clear the 4 tabs. The 5th tab, on the diagonal, you want to pry up on the "top" to get the tab to start straightening out, then bend it all the way straight and clear the slot. All the guts will be attached to the "top half" of the case as it's laying in this photo, and the other half, which the sides are part of, is a cover you can set aside. Flip it over and you're looking at the gearbox.
Take out the 4x T15 screws and pry it open.
So the worm gear motor spins the small gear, then the big gear. A tab on the bottom pushes against the silver clockspring to return to center. The tab on the top interfaces with the white lever in the first pic, which eventually actuates the lock.
PN on the motor. Top number resolves to a number of listings like OPs. Since all the options I could find ship from China, ETA is 01/19-01/26. I'll follow up with whether the motor fixes my power lock.