Product review (5 stars): Finally, a Rinse Aid Cap!  Such an easy replacement.  Why didn't I do this earlier?
This Whirlpool Rinse Aid Dispenser Cap is a perfect fit for our original one that somehow managed to come loose, fall into the bottom of the dishwasher, and melt in the heated dry cycle.  For the past few years we ran the dishwasher without a cap.  I stumbled across this by accident.  Am I glad I did.  What a difference it makes to have everything working as designed.  (And I get to start using up some of the many bottles of Rinse Aid I've accumulated over the years; they're just taking up space underneath my kitchen sink.)  :-)