I am not sure what you mean by overhead window. Do you mean the hatch in the v-berth? If so, mine leaks as well and it is due to the gasket shrinking over time. I am planning on trying to remove the plexi/plastic and re-bed with silicone. I have on my list of things to get done this winter. In addition my windshields both leak a little (non-opening type). I need to disassemble them and install new gasket material which I have already secured. These gaskets are dry rotted and despite previous owners trying to silicone them they still leak a bit.