Following are the common causes of pump seal failure or leakage;
1. Dry run of a pump, while suction valve in close position.
2. Starting the pump without priming.
3. Dirt or foreign materials in the fluid.
4. Sudden cold or hot fluid introduction in the pump.
5. Imbalance shaft of the pump.
6. Vibrations in pump.
7. Sever cavitation in pump’s casing.
The best is to develop start up checklist and follow it