If you see water leaking out of the bottom of the pool pump assembly, it's a good indication that you may have to replace the shaft seal within the motor pump assembly. As shown in the pool pump cut away, the shaft seal is located in the motor pump assembly behind the impeller. Although this description is specific to a Hayward pool pump, many of the steps can apply to other models of pool pumps.
You will see the pool pump motor wiring and capacitor. You will have to remove the capacitor to gain access to the end of the motor shaft. Capacitors store power. To avoid a possible shock, lay a screwdriver across the two leads to short out the capacitor. These capacitors sometimes burst when shorted out, so it is a good practice to place a cloth over the capacitor and to wear eye protection.
Grab the seal on the pool pump impeller and twist it off. Make a note of how the seal is positioned on the impeller so you know how to place the new seal. It is possible to place this seal upside down. Note: You may have to also have to remove the metal collar if the new shaft seal also has one. Several people have written in saying that the new seal won't fit because they were trying to place the new collar on top of the old one.
Replace the four bolts evenly. If bolts were numbered 1 though 4, replace bolts in this sequence - 1, 3, 2, 4 - to ensure that the motor is set properly inside the housing. Loosely tighten bolts in this sequence, then go back and tighten them down again in this sequence. If pool pump has 6 bolts, replace bolts in this sequence - 1, 3, 5, 2, 4, 6.