I had a similar problem w/ one of my elec. pumps...the plastic coupler was slipping on the motor shaft. The motor ran but the pump was barely pumping.

I took it apart and cleaned it...put some scratches on the motor shaft and CA'd the coupler to the motor shaft. It worked for a while, but then it started leaking...

The replacement leaked from day one...

Using a hand crank pump now...has been working fine for several years...(hope I didn't just jinx myself )