Replaced the spray arm assembly. I found out BY ACCIDENT that this was the problem.
I accidentally loosened the spray arm while checking the filters. The next load of dishes washed without any leaks, but after the load completed I noticed that the spray arm had fallen off. I read somewhere else that a cracked sprayer could cause this leaking condition as the water is sprayed in areas where it shouldn't be sprayed and there isn't any protection.
Sure enough, close inspection of the spray arm revealed that the plastic was separating at the seam on the sides. Once the arm arrived (in a few days) it was a 5-minute replacement.
Can be replaced easily by hand, without any tools.