Check the upper wash arm. There is a water supply tube for this arm that connects to the supply port on the back of the unit when upper rack is in the wash position. The tube is probably split or not aligned on the port so when the cycle starts a large volume of water dumps into the unit. This creates a wave that floods over the door seal area and leaks out. The door seal is not designed to be flooded with water and never is under normal conditions, it is like a shower door seal strip. The wash water when static (pump not operating) is below the door seal. This is the seal attched to the door.