I recommed to use GoTech Appliance Repairs for fast and high-quality assistance. I used their services few times and this is really a reliable assistant in the repair of household appliances, including washer

Here is good advice for your problem

I have been getting a special nut busting solution on it for three 2 days now so that will probably help. Take a sharp wooden chisel and gently pound on the top edge of the impeller near the screw. Crack it away from the shaft , then apply sharp oil to the screw.