Well, it works!
I went to the hardware store and bought a small package of compression springs that are 1 3/4" long by 3/8 diameter and made of .035" wire.
The original spring is on a pin that'* swaged at the bottom end to part of the linkage. At the top end it goes through a hole in another piece, so the spring is partially compressed and captive between the two parts.
I was able to bend the top part up enough with a pair of pliers to release the end of the pin and the spring. I simply slipped the new larger spring down over
the existing spring, then compressed them both and bent the part back down. Looks just like it should have come from the factory!
Put the latch back in the door and hooked it up and the augmented spring easily returns the linkage when the lock is activated. Problem solved, at least until the linkage gets even stickier...
The door'* back together now, little worse for the wear. Works fine.
Being very familiar with the way it works now, I tried pounding on the rearward portion of the driver'* side rear door to see if I could get the linkage to drop with the weak spring and it did! So, I at least know what'* going on now, and I'll probably take it apart and do the same fix, since I'd rather not have to do it again any time soon.
Randman, thanks for all the help! Your guidance got me going again a couple of times, for sure.