Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
Although water leaks are sometimes very hard to pinpoint, as it could be the windshield seal, doors, or drain channels, there has been a service bulletin on the mirror seals that may be causing the leak.
Here is a link to a PDF file that you can download, which has the TSB for that. It would be worth looking into, but please don't forget to come back and hit the accept button, that is the only way we get paid, thanks