Product review (5 stars): A quick, inexpensive fix...
When my washing machine started giving me grief and the upper portion of the agitator wouldn't turn, I thought I was going to have to trash my six-year-old Whirlpool and get another one.  I don't trust repairmen!  Thanks to folks on the internet who have shared their experience and expertise, my $500.00 potential dip into my emergency fund was instead reduced to a $6.23 quick fix that took less than 15 minutes start to finish.  The parts I ordered arrived in just three days, they were genuine Whirlpool replacement parts and instructions were included.  The instructions were a bit vague - just a couple of lines of text and a couple of simple sketches - so I would definitely recommend printing off detailed instructions from elsewhere on the internet.  A simple search of "Whirlpool agitator" will pull up a dozen sites with all kinds of pertinent details.

As an added bonus, I noticed that all of the noise I'd been experiencing from the washer that I had simply attributed to the washer's age was alleviated after replacing the cam and dogs.  She sounds like a new washing machine again.