I have a Kitchenaid dishwasher that is about 5 years old. It worked perfectly until about a year ago, when it began leaving a slight greasy film. Nothing else has changed--the setting on the hot water supply is the same, detergent the same, water is the same, etc.
I have tried different detergents, including liquid, and that doesn't help.
The rinse agent container is full and functioning.
I have cleaned all of the traps and screens.
I have checked all of the holes in the rotating sprayer arms.
I have run a couple of cups of vinegar through it.
This past weekend I removed the dishwasher, flipped it over, and dismantled the entire pump and drain system. All of the lines were free and clear and all of the impellers were intact.
The only thing I can think of now is that the heating element is not working. It does seem as though the dishes aren't drying as well as they did in the past.