I had a similar problem
I once had my 21' centerboard trailer sailor fly off my trailer while tooling down the road. The boat was ok but developed a leak which sometimes was severe. The leak was not consistent - it only occurred when the board was down.
I finally discovered that the pivot bolt was several inches back from the leading edge of the board and when i dropped the board, the forward segment of the board swung up into the trunk. In the trunk was a stopper bolt that was intended to limit the travel of the board so that if the hauling wire snapped, the board wouldn't swing down and have the upper portion of the board swing into the trunk and smash it.
When the boat flew off the trailer, the board must have swung down and the forward portion of the board swung into the bolt with enough force to tear up the fiberglass around it creating the leak. I fixed the glass and replaced the bolt. Never leaked again.