Product review (5 stars): Whirlpool Detergent Dispenser
This item is made by Whirlpool, is a factory replacement part and fits my Whirlpool made Kenmore dishwasher like a glove.  I was having a problem with the Jet Dry rinse aid completely emptying after only like a week or less after filling it.  We run our dishwasher every day with the four of us using so many dishes and glasses. The cap was in good condition, with no cracks or other defects in it or the O-ring of the cap.  The only thing I could think of was this dispenser.  There would also be a small trickle of dried Jet Dry coming from the dispenser in between loads.  Checking around at some of the appliance repair websites, my initial suspicion was confirmed.  So I ordered this and installed it.

Looking at the rear of dispenser, a small solenoid releases both the detergent and the drying agent (I imagine at different times in the cycle).  My best guess is the solenoid was not closing the valve for the Jet Dry completely.  The dishwasher is about 4 1/2 years old now.  I have run about 5 full loads through the dishwasher and the fill indicator has hardly moved at all, just like before my problems began, so it looks like I was right about the repair/replacement.

**Edit 8/18/13**  I'm getting about a month to six weeks out of a full load of Jet Dry now, that's with using the dishwasher almost every day.  This is still working great, I know now that my initial assessment was correct.