This is no way advise on how to do this, just sharing what I did, so if you hire a repair man you know what to expect.

My pump was sucking in water too, but working with motors I could feel the grittiness of it when I turned it. Yours maybe just the inside piece thats replaceable with the fins, isn't seated correctly or worn.
I fixed mine by replacing the circulation pump.
I pulled it out at first and checked the solenoid water valve in front down on the left corner (followed the water supply line), and it was clear and water was getting past that, I figured it couldn't be the heater so it had to be the pump, pulled the dishwasher out, killed the circuit breaker to it, shut off water disconnected it, took out the inside and the two retaining screws in the drain area, and turned it upside down, took the two tin sides off, (took pictures of everything along the way), two long screws in back holding the bottom plastic on, there are four screws in front, there are two plastic covers over the door hinge- connection, pulled on the spring to gain some slack and unhooked them and tilted the bottom cover up on one side. Carefully disconnected two hoses (one has a retaining clip), and all the electrical connections. carefully pulled out pump- heater-drain unit out, one of the pipes going to the drain has no wire band and slid right off, the other pipe going to the heater has a band you have to clip and replace. pull out two screws n heater, and pop off. replace pump and reverse order.

I repair large printers and copiers so this didn't scare me to work on it, plus my wife refused to look at something cheaper, the pump cost more than a new Kenmore, but she wanted her Bosch, its a five year part or thats how long they I have been seeing they last, so hopefully I wont have to do it again for a while. Though its not for the faint of heart BUT if I couldn't get it apart to see if I could replace the pump I was no worse off, though the kids didn't like doing dishes by hand.

SHU4305 model