After investigation, it was found that the rear vents were not closing properly. As James explains in this video, although they may cause water ingress from water can splash up onto them.
Because of this, it can make the problem hard to diagnose, but we have seen a number of Audi TTs with this problem and consider rear vents to be a common on this model of car.
There is also a bung missing which is letting in water where a cable enters the arch.
We also found that the drainage system for the roof was blocked. James demonstrates that there is water in the footwells after it has overflowed. We recommend removing the seats and lifting the carpet to dry underneath to ensure they are completely dry to prevent electrical problems, smells and mould.
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