When I took apart the agitator, I could see that the thrust washer was broken. I ordered a Cam Agitator Repair Kit (that included the thrust washer along with new dogs and new cam, because I have read that it is common for them to wear out; and an Agitator Bolt (because before it completely stopped agitating, the bolt kept backing off). I simply changed out the parts, put it back together, and reattached it to the washer.
I didn't realize that grease would be needed for the Thrust Agitator. I did not have any, so I used WD 40.