> Since the receptacle was old and tired and I already had it out of the
> box, I replaced it and two other elderly and infirm receptacles on the
> same circuit. Everything works.
> What was wrong?
My guess is that the old receptacles were of the "strip & stuff"
Basically, you strip the insulation of the solid conductor wire, then
stuff the bare wire in the hole in the back of the receptacle.
The wire is retained in the receptacle by using the Chinese finger
puzzle technique on a spring. Basically, a one way clamp.
If the receptacle carries enough load for a long enough period of
time, the spring gets tired.
Replacing the receptacles with a better grade that has side wired
screw terminals should solve the problem.
One other possibility I really don't want to think about.
What is the age of the home?
Any chance we you have aluminum wiring?