What is the cause of dishwasher vent leak?
Does the water appear clear/clean, or does it have food bits and/or detergent in it?

My guess is one of two things:


The seal on the flap has degraded and the high-pressure jets are now able to force water in under the flap.
There is some "ledge" in this assembly in which water can collect and puddle, and doesn't dry during the dry cycle (possibly because of the extremely humid air passing by it; there's no capacity in the air to hold any more water).