Gasket Replacement on a Pentair Whisperflow Pool Pump

I recently noticed that my pool water level was dropping faster than normal and there was a large wet spot downhill from the pool pump.  After looking at the pump while it was running the problem was obvious.

Water spraying out between the pump flange.

I ordered a new gasket (Pentair part #357102) and a new diffuser o-ring (Parker #2-238) and opened it up to replace the seals.  The only tools you need are a 9/16" socket and a 9/16" open ended wrench.  After shutting off the power, just remove the 6 bolts holding the two flanges together, grab the motor and pull straight back.

Disassembled pump with old gasket and missing o-ring

Once you have the pump pulled apart, lift the old gasket out of the groove and replace with the new one, (flat side into the groove, crowned side facing the other flange), replace the diffuser o-ring (mine is missing in the picture above).  Here's a comparison of the old and new gaskets.

Lubricate both the gasket and the o-ring with some o-ring grease and slide it back together.  I used the two through bolts to help guide everything back into place. Tighten the six bolts a little at a time in a cross pattern like the lug nuts on your car.

After the parts arrived I was able to fix this leak in about 20 minutes with a total cost of around $15 for the two seals.