When the shaft seal leaks, water gets to the pump motor front bearing and it eventually siezes. Most people replace the pump motor at this point. The motor can be repaired. I learned this procedure from a repairman who let me watch. Good thing as he is no longer in business. My pump motors (Polaris and pool circulation) are 20+ years old and both have been repaired 2-3 times. Here's how.

1) remove motor w/ pump attached. Wiring will need to be disconnected from motor to allow work on motor. PIA.
2) remove cover from rear end of motor and there's a flat on pump shaft that can be grabbed w/ vise grips to hold the pump shaft.
3) Holding pump shaft, use a strap wrench or special pump wrench to turn the pump impellor (CCW I think?) and remove impellor from pump shaft.
4) There are 4, long thru-body bolts that hold the motor assy together and must be removed. They are long small diameter bolts and some may twist off. Apply heat and take your time. I've always managed to get 3/4 out, and have left the 4th off. The sheared ends can be drilled out and replaced but machine shop help may be necessary.
5) Remove motor end nearest pump and you can access the siezed bearing on the motor rotor shaft assy. You will likely need a bearing puller to pull the bearing off the shaft. Clean shaft w/ emery cloth and lube to allow bearing to move easier.
6) Replace bearing and reassemble. I found the bearing and pump shaft seal at Warehouse Pool Supply in Houston. They are available on line from numerous sources.

You can also replace the bearing at the rear end of the pump motor but it rarely fails.

If you watch the pumps and note when shaft seal begins to leak you can avoid this repair as the shaft seal is readily accessed for replacement.

good luck