Replace it. I think consumer reports has a repair/ replace timeline for each appliance and it was about 4 years for most (but not all) appliances.
If you subscribe to CR, then go look up what I am referring about.
http://www.consumerreports.org/cro/magazine/2014/02/repair-or-replace/index.htm
You have to be a subscriber to get the info on dishwashers.