Product review (5 stars): Be sure you need before buying
To diagnose a leaky dishwasher, I suggest these steps.
1) Aggressively clean around the seal area. All around the door, especially bottom center. I found a lot of gunk here, leading me to believe I had a seriously deteriorated center gasket. If leak persists then:
2) Take the corner gaskets (this part) out and vigorously clean them with a stiff brush. Reinstall them and if leak persists or if damage is evident then:
3) Replace corner gaskets with new. I replaced mine and saw that they were really dirty. Probably could have just cleaned them before I bought new. If leak persists then:
4) inspect door seal.  Replace if damage is evident. If leak persists then:
5) leak could be somewhere else than the door. In my case I had slight discoloration on the bottom panel which told me it was a door seal issue somewhere.