Washer wouldn't agitate, but everything else worked.

This was a very simple repair. I Pulled straight up on the agitator until it popped off. Then unscrewed the bolt that holds the coupling in place. Due to some corrosion and crud, it took a little effort to get the coupling off. Then I spent a couple minutes cleaning the tub and shaft. The new coupling slid on easily. I attached it with the new bolt, then put the agitator back on and pressed down until it snapped into place.