Re: 1 month of a new GT and..
Mine had a leak into the boot area when new, it was dripping off of the storage box on the O/S, I traced it to a small hole (and i mean small) in the sealant under the roof gutter inserts. I carefully lifted the insert out, its only a push fit with a small sticky pad at the end, be careful not to bend it too far as although the paint is really flexible it must have a limit, I could then see a tiny hole in the mastic where the roof joins the "D" pillar. I had first stripped the interior trim but couldn't find it. I have no faith in the dealers and as it's my trade I was quite happy to sort it myself and time wise it was probably quicker.
In 37000 miles (13 months) I have had a faulty clutch replaced, after two weeks, and just the water leak, a seat creak and a rattle, only the clutch done by a dealer and they badly damaged the car.
So really happy with the GT, service it myself (use a friends diagnostic reader) it has no rattles or leaks and at this point I can't find anything i would like to replace it with.