Well, I was able to take a closer look at the derailleur, this time with more appropriate lighting. If you look at the last photo above, there is a bit of metal from the pivot arm that extends at the bottom and covers the lower left corner of the spring (according to the photo.) It is what the spring contacts to create the tension. Unfortunately, that little extension has busted off mine rendering my derailleur currently useless. I'm sure I could take the approach of trying to scavenge a replacement pivot arm but I don't have a junk derailleur bin, just a couple of tubes with holes. $25/shipped for the same replacement derailleur. I'll keep in mind the way to "fix" it for next time, thank you FBinNY.