The mechanical seal is located where the shaft of the motor goes into the back of the pump. It is very difficult to see and often is completely obscured. If you cannot see the shaft of the motor, then the best way to check for a pump seal leak is to take a mirror and place it under the pump. Look for water trickling down the back of the seal plate.
Mechanical seals can fail due to old age, water chemistry damage, pump overheating or improper seal installation. If the mechanical seal fails, it is very important to get the seal replaced as quickly as possible. This is because a leaky mechanical seal can allow water to travel up the shaft of the motor to the front motor bearings and quickly ruin them. When the bearings go out, it’s time for a new motor or a new pump. It’s wise to replace a mechanical seal as soon as it begins to leak. It is also a good idea to turn the pump off if possible until the repair can be made, to keep further damage to a minimum.
Every pump has some sort of a gasket that seals the two halves of the pump where they bolt or clamp together. Over time these gaskets get old and hard and begin to leak. This usually results in water leaking off of the bottom of the seal plate.
Putting silicone or putty on a pipe leak is not an acceptable repair. It must be replumbed.
As a pump gets old, the material will develop stress cracks. Usually if a pump is this old, it does not make sense to spend several hundred dollars repairing it. It’s better to spend the money on a new pump with a full three year parts and labor warranty.