I have pulled out several 1970s and 1980s 4.5v and 12v motors/trains from my childhood for my children to play with. Everything is working pretty well, except that we have recurring contact problems plugging the cables into either a battery box, motor, or transformer. A lot of wiggling is needed to make the connection, and it's hard to keep the motor turning without holding the connector in place.
Since the plugs just seem to be metal cylinders, I assume the sockets must have some kind of spring that has worn out. Do you have any advice on rejuvenating them? I don't want to try to replace all the motors and power supplies :)