I would try this before starting a new thread -

Take your car to a carwash, and make sure to bring several quarters with you!! Before getting out of your car, turn your heat or a/c on full blast, and get out of the car. Soap up the car and watch for any bubbles that may form around the windshield, door openings, window trim, etc. Where bubbles are forming is where water is getting in when the cabin isn't pressurized (I.E. when the heat/a/c fan isn't running). It may not pinpoint where, but it will get you in the general area of the point of entry.

Old trick I learned while working at Ford dealership body shop to isolate wind noises ;)

Yup, Sandrock has it right. This is a recommended method from professionals too.