The impellar should slide in and out very easily and even have some wiggle room.
When the sand got in there and bound everything up it scratches the hell out of the motor inside. So you have to put something in there to smooth out the roughness and get any sand out that is stuck in the palstic..
What i have done in the past is place some sand paper on something round. And move that in and out of the motor hole and work it around the circumference. A wooden dowel, or even a chapstick case works really well. And about 220-320 grit paper.
If you want to, bring me the motor and impellar and i will fix it up for you.