Fortunately I cannibalized the thermocouple from the old extruder, hooked it up, and the problems went away, which means the thermocouple itself had gone bad. Simple fix.
Every time these fixes come up I do a little cost count in my head. Is this pain and headache really worth having a 3D printer? The answer, of course, is yes. Every time. The expense itself has been covered by my various ventures, and just having those ventures is something I could not do without 3D printing. Having a 3D printer has changed my life in a very good way. I'm not saying having a 3D printer will change everyone's life but it's definately been worthwhile for me to spend a couple hours jimmying a fix out of the ol' bot.
Of course if anyone ever builds a 3D printer that works well and takes no more maintenance than my inkjet printer, I wouldn't complain about owning one of those.