94 Golf no start in hot weather (no crank)

I have a 1994 golf, 2.0 L, 5 speed. I have recently been driving my car without problems when a hot day came around and my car did not start. Today however was a bit cooler and when i came home from work i decided to give it a shot and what do you know...it started. I have looked in to this problem alot since it did not start. The main problems seem to be with starter motor/solenoid, ignition switch or fuel system. I know there is power to fuel and power to solenoid. i have just replaced the battery and have checked the connections. i did read somewhere that when it gets hot out the brushes(i think) expand a bit in the starter motor and dont allow it to move. i did not try tapping it with a hammer. When the key is turned to the start position headlights dim. all electronics work in the car.
Any suggestions would be much appreciated. thanks

sounds like a starter. a rebuilt one from napa is about 120.00