After clenking all the gunk out of my dishwasher, the arm on the bottom of the upper rack is still not spinning.

Considering that the other two arms, the upper and lower ones are spinning, will this be as simple as just replacing all three arms? (We llive in an area that's known for its notorious hard water, and many of the untopuched parts of the dishwasher were heavily calcified/covered in crud when I took the arms off.)

Is there anything besides a clog that would cause 2 arms to spin but not 3?

Also, should the water level be ABOVE the heating element, or merely close to it? Someone else suggested that this meand I have a water valve issue, but I'm not convinced of that.

Given that my heating element is fairly well covered with mineral deposits, should I replace it? (I was hoping to wait to do that until I purchased a water softening syste,)