Sometimes it takes soaking the agitator in hot water to dissolve gunk, sometimes it involves brute force, but be careful because you can hurt yourself badly.

If you cannot get it separated then you may have to purchase a new agitator, but try the other methods and get a big, strong person to help, again being very very careful.

I am trying to change the dogs in my washer agitator and I can't get the top and bottom separated. Do you have any idea how I can get them apart?