if you have your old car sitting in your garage maybe you can knock down this part :)
but you will found the dificulty and will have a great headace to find such as type of DC pump which is entirely build from plastic, especialy for the MOTOR,
To do this we need a trick to make the METAL part is COROTION proof and as much as possible remove the dirrect contact with the ETCHAN liquid.
after complete covering the metal shaft with heatsrink tube, you need to reasamble again as before
First Step you need to detach the motor body so you can get acces to the motor shaft which is this part is linked to the propeller to circulated / pumping the water
The point here is : YOU NEED TO COVER THE METAL SHAFT AT THE MOTOR USING MATERIAL WHICH IS MADE FROM RUBER / PLASTIC (IN MY CASE, I AM USING THE HEATSHIRK TUBE) COVER THE METAL PART ENTIERLY COROTIONLESS (THERE IS NO DIRRECT CONTACT WITH THE ETCHAN)
I don have a good picture for this steep but I am attaching my Hand Sketch and I am sure this will be easily understand.
I am re attching the process of the deasembling the motor and clearly shown which part need to covered with heatshrink tube.