The design of the sunroof on the 850 is not to preclude water entering around the closed sunroof, but to efficiently remove the water that does come in through four drains located at the corners of the sunroof tray. If you are absolutely certain that the car was not driven in the rain with the sunroof open, then the drains are the most likely culprit. If the drains become clogged, this can cause water to spill in over the lip of the tray. This is easy to check just by opening the sunroof, and pouring some water in the tray and see if the water drains out through the drains. If not, then clearing the drains should fix the problem.

Phantom