Don,
You have been complaining about that aluminum wiring for years. Time to either pull it out and replace or convert all the connections with the approved copper pigtails.
Because the outlet was not being used does not mean that there was not current flowing through the circuit.
This particular circuit fed all four of the bedrooms.
Went on call about a week ago where customer had one kitchen outlet on one side of sink with transformer of cordless phone connected. Had a light fixture plugged into outlet on other side of sink. Customer said outlet with phone connected was intermittent, wouldn't keep phone charged. Also said the lamp would sometimes take about 10 seconds to come on. Of course every thing worked fine at the time and would not fail for me.
My first thoughts were that the quick connect holes were used wire the outlets and a bad connection had developed. I pulled the outlets to find that not to be the case. House was about 30 years old and customer said that no electrical work had ever been done. House was so old that it had fuses not circuit breakers. I could tell that there were other outlets on the circuit but I could not find them because there was so much junk in the house. There was a path through the dining area and living room, everything else was cluttered with junk. So much junk that if you could see an outlet, you couldn't get to it.
Evan though the outlets were working at the time I decided to replace them. I remove the fuse and replaced the outlets. After replacing the outlets neither would work. My meter showed 8 volts at each outlet. Now I am thinking faulty neutral.
Remove the panel cover and checked the neutral. All the wiring, including the hot, look good. I remove the fuse and check the incoming center terminal of the fuse holder. Had 120 volts. Put the fuse back in and check the shell of the fuse holder and had 120 volts going out. So I have 120 volts in and 120 volts out of the fuse, why do I only have 8 volts at outlet?
I touched the hot wire out of the fuse holder and about one inch of insulation crumbled. Remove the wire and the end of the wire was almost entirely burned away.
Apparently there was a loose connection that had been arcing for 30 years until it finally burned the wire into.