On My 2006 C387
it came from the factory with a solar vent installed. I previously installed two solar vents on my Hunter 35.5. In checking the vents one day on the Catalina, I discovered that they had been installed incorrectly and although the fan would run, no air was moving. Pulled it apart and discovered that the adjustable sleeve had been glued so that the vent couldn't be turned on. Checked a neighbors C387 that is about a year earlier boat. It was glued the same way. That is one way to keep them from leaking water.