Take the glass out and use it to trace a pattern on a piece of 1/4" wood. Put heavy chalk on said wood and gently place it centered in the cut out from above- attach a handle in the middle of the board- the placement must be done carefully. Gently press down on it once it's in place, then remove it slowly. Look on the frame or rubber gasket in the hole and see where there is no contact. Beef up this area and you should fix the issue. Conversely, you could strategically add some material to the glass in that spot as well if needed. Check and clear all drain holes- test them as well to make sure they themselves are not the source of the leak. lastly, check the opening in the roof for square and level. Measure from one corner to the furthest corner, then do the other side. The #'s should be equal. If all else fails, bring it to a sunroof shop. They can always cut it out and install a slightly larger one that doesn't leak. If you never plan to open it, in a pinch, you could silicone the seam from the outside. Good luck!

Cadillac came out with a sunroof on the 1938 Fleetwood Sixty Special. They leaked. Somes things - especially at GM - never change.

My 1995 Chrysler had a moonroof . . . kept it until 2007 and it never leaked a drop. My 2007 Ford Taurus has a moonroof . . . has never leaked a drop.

If Japanese and European sunroofs don't leak, why do they all have roof drains?

All sunroofs leak.

ALL car makers anticipate that and install four roof drains to remove the water. When a sunroof leaks into the car, it's a sign the drain are clogged.

Read this post on how to fix it

http://www.familyhandyman.com/automotive...

Probably because it's raining.

Check the drain holes

Because american cars have internationally renowned poor build quality.