Splash pad pump wont prime

I'm a happy pool owner but helping a friend with their splash pad. It's been sitting for about 18 months without running. I cleaned the basket, lubber the o rings, cleaned the cartridge filter. Replaced the multiport gear assembly and was able to get it to prime and cycle.

However the pressure was very low (4 psi). After letting it run for about an hour it would no longer cycle as the pressure dropped to zero. I cleaned the pump basket and cartridge again (yes it needed it). Reconnected everything and now cannot get the pump to prime.

After reading on this site I though perhaps the impeller was clogged but upon disassembling it was perfectly clear and free from cracks, etc.

I'm thinking the problem is the pump but wanted to get some more informed opinions. The pad and equipment is about 3-4 years old.

Thanks!