I have attached a close up pic of the pump gear, you can see the metal had been cut and pushed down, I'm thinking that's from the worm gear turning against the pump while stuck, the pump gear being softer, takes the damage.
If I can find out the width of a good worm gear I could measure and see if the thread has worn down, but I'm told that's way harder than the pump gear so shouldn't get too damaged against a softer metal.