Sounds like it could be your starter motor contacts (inside the starter itself). The click of course is your solenoid making and engaging the flywheel, but perhaps your brass contacts are just worn enough to a point not to make the motor rotate after the solinoid is made. Sometimes, this is a on/off process. After time, the turning and pounding of these brass contacts during cranking wear down the contacts to a point that you start to loose a good contact area, therefore the starter motor will not spin. Sometime's it will work just because you have moved the postion of the contacts inside. If this "is" your problem..your time is running out.