I took apart every connection and component and cleaned things up. Still keeping the box open to let things dry out before the weekend.
Threw a dab of dielectric grease on all connections.
All of the grommets look to be in good shape.
I have a new gasket coming, but I don't think that's where the water was getting in.
Note: I took the plastic cover and set it upside down and then filled it with water. After a few minutes, water began to seep out of the inspection cap threads. That looks to be the culprit. The rubber Oring seems a bit dry rotted and thrashed. I'm going to flip it over and grease it and see if that cures it. Does Yamaha sell these O rings?