As I said in the last update for this, I rebuilt the extruder. Yay!
But there is a slight problem: the extruder, for some reason, extruded for a while, but then just stopped. I think I just need to tighten it down better (I did it by hand first). Ugh. This run-it-for-a-bit-and-then-it-breaks-and-I-have-to-fix-it routine is really getting on my nerves.