I run an electric motor repair shop and although we tend to stick with larger industrial motors we do our fair share of "break even work" for the occassional residential customer who needs a fan or pool pump motor. Most of what was said above is true. There are generally 2 types of motor failures - (1) Bearing failure. As the bearings near the end of their life cycle they will add parasitic drag to they motor making it work harder to maintain its rated RPM. With more load from the bad bearings comes higher amperage, more heat, and more slip (rpm loss). This will begin to affect the insulation integrity int he windings which leads us to the 2nd type of motor failure - (2) Windings shorted. This is an all or nothing type of failure. The winding insulation will degrade and at a measurable value ofver time but the motor will run until the windings either short to ground or turn to turn, phase to phase (in rare instances they will open rather than short and not be detectable by meggering, surge testing, IR, PI testing method). Usually whent he windings fail it is not economically justifiable to rewind a pool pump motor for a motor repair shop. Its just to time intensive. There are a few shops int he US that specialize in rewinding small motors very economically but I can only think of one off hand. Replacing bearings, seals and reinsulating the windings can be done very quick and economically as long as the housings and journals dont need any machine work. Hope this helps and I hope your still awake, I'm not.
The suggestion to check the amps on the motor is an excellent one. As the filter clogs up the motor will draw more current. Any restriction on the inlet or outlet will do the same just like bearings going bad, the motor sees it as more load. And all pool pump motors run hot. They are usually rated for at least a 40 degree celsius temp rise over ambient.
