Upper rack of dishwasher was not cleaning well.

We noticed spotting and just poor cleaning performance in the dw. It was particularly bad on the top rack. After removing the racks, it was clear that the gasket on the water fitting in the back of the dw-upper was about half gone. No tools were necessary. I just unscrewed the ring nut-gasket and replaced it with the new one. Finger-tight. If the old nut was stuck, a pair of pliers would have helped.