Water leak

A window seal can be blown, or a runoff channel is clogged with dirt and debris. you can pick up color tabs at any parts store, place them around the roof line, and run water over them. Each tab is a different color, and depending on which color leaks through it will indicate where the leak is. You can fix it on the cheap with some silicon RTV, or if it is a blown window seal, call up any of those window replacement companies to reseal it.