I would venture a guess that the majority of the heat he is experiencing is from a worn socket(poor connection).
It could also be backstab connections. They tend to get loose over time, in my experience, to the point that you can sometimes pull an outlet out of the box and the backstabbed wire pulls right out of the back of the receptacle. In my old house, I went through and pigtailed all of the connections to the outlets between the load center and the garage. I made up the pigtail with a wirenut and a short length of wire. I connected the pigtail to the outlet using the screw terminals. That way the circuit isn't daisy-chained through the outlet anymore, and the connection to the outlet is the more reliable screw terminals.