This washer is no longer cleaning the dishes. The first symptom was the detergent door not opening. I cleaned all the gunk out of it and now it's opening, but detergent remains after the cycle.

I've taken apart and cleaned the lower end of the washer, the filter screen and associated parts. I've replaced the upper and lower spray arms, all to little avail. The water level appears fine in the tub, so I don't think it's a fill valve issue.

I do notice that the upper arm does not appear to move very much, as when I open the door in mid-cycle, it's stationary, while the lower arm is still spinning.

Might this be caused by the pump that pumps water to the arms?
Any advice would be appreciated.
Thanks.
Brian