Catalina 350 International Association

This leak is on the port side about halfway between the port light and the nav station. It starts up near the hull/deck joint. It is not near a stantion location. I noticed a small stain last fall but it worsened over the winter.
As you can see in the pics it appears to originate near a bolt which I assume is for the joint. I will try to flood with hose to check source. I'm not looking forward to removing rub rail to get to joint.
Anyone been here?

I would look closely at the stantion and the cleat. Use a dry erase marker (or a kids washable marker) in the areas you suspect water is running, marking the fibreglass (not the wood). If water runs on the area marked it should be visible with running color.