A common place for the leak is between the sunroof frame and the roof. If you look you could probably see a gap. I could, on both my sunroofs. To test if this was leaking, I ran some black electrical tape over the gap, with a view to doing the job properly with black Sikaflex down the line. My car is now dry and the electrical tape is such a neat job I'll probably not bother with the sealant till next summer.
I haven't put my carpets back yet though. I'll wait till I'm 100% sure its not leaking.
Cheers
Andy