I have a Sta-Rite JWPA5EL-2A pump with AO Smith motor and a leaky impeller seal. I've obtained the new seal but can't figure out how to get the impeller off the motor shaft to get at the seal. The store where we bought it "thinks" it's left-hand threaded onto the motor shaft, but can't get it to unscrew. Does anyone have suggestions for how I can do this without destroying the impeller?