My trusty old Kitchenaid KDS-20 dishwasher isn't draining properly, leaving water in the bottom of the tub. I removed the drain line from the dishwasher and the garbage disposal and blew through it, so it's not clogged. I removed the drain solenoid valve, and it is free of obstructions. It also snaps open smartly when the timer applies power to it. I removed the coarse and fine filters inside the tub and cleaned them. So, I'm assuming I need a new drain impeller. However, the wash impeller is stuck on the shaft, so I can't remove the wash pump housing to get to the drain impeller. I tried gently prying on the wash impeller, but cracked a tiny piece of it, so I need to find a gentler way to break it free of what looks like a rusty corrosion product around the shaft. Any ideas?