Product review (2 stars): O-ring a poor fit
The o-ring was too bulky.  Would not allow the "dust cap" to be reinserted.  With a fabric softener dispenser this fit is critical.  I had to reuse the old o-ring although it had a few nicks.  At a glance the rings looked the same, and it fit the dust cap fine.  But the cap could not fit the bore of the agitator with the new o-ring in place.
Dogs are not identical to originals, but seem to get the job done.