We have a three year old dishwasher which has been spotting/filming the glasware (BAD) for the last two months. The "jet dry" dispenser hasn't dispensed anything, either. It's still full. Where/how does the rinse agent some out of the machine, and how would I determine if it's plugged?
You failed to mention the manufacturer. Whirlpool (includes Kitchen aid) and Kenmore made by Whirlpool(model prefix 665) had a problem with the dispenser. Not a big job to replace. Problems with too hot temp water can cause the same problem. If water is too hot it evaperates too fast and doesn't allow water to sheen off. Water shouldn't be hotter than 140f.