If the motor is still working, I would suggest just giving it a good cleaning. The rubber diaphragm could be ripped, or it could just be the check valves it should have one on each side, they work together to keep the water pumping out, from the amount of debris in the pic, they could just be stuck open.
These are very simple pumps and work really well, pump just about anything as long as it can make it through the two ports.
I was trying to make one out of a windshield wiper motor...it pumped a ton of water, but just like the one above it hadf a pretty good surge as it works so you might need to place something on the hose to keep it where you place it.
Awesome pump out you will be happy once you get it going.