First, I just want to be sure that you had replaced the suction tube. I noticed that you thought you had some cracks in the PVC pieces, so I am assuming that you replaced the tube with a black iron pipe or something similar. Correct!
You can also check the bypass valve. It is behind the large nut on the side of the pump. If there is something stuck behind the plastic poppet, that is holding the valve open, the pump won't generate vacuum, so it can't pump. Did that found nothing!
You can also remove the pump from the tank by removing the 4 bolts on the inlet flange and check the screen at the inlet. At the same time, you can place your palm over the inlet of the pump and turn the pump on to see if there is any vacuum. Did that found nothing!
Make sure that the battery cable is on the right connection to the battery. If you reverse the polarity, the pump will run backwards. It sounds like it should be working, yet it can't pump if the motor is running in reverse. Used the tractor battery and my jump starter, doubt I crossed them both times but hey I'm old.
If all the above fails, then yes, you should rebuild the pump. It will replace the rotor, rotor cover, rotor key, vanes, bypass valve, screen, and all gaskets. You could have a gasket that is just not sealing very well and is allowing air in. Running fine since replacing the suction pipe.
Keep me posted on what you find.