I read some problems on the AW and I couldn’t believe A8L D3 clogged drains could cause the water to come into the car so much that the insurance totaled the car instead of fixing it.
Clogged Sunroof Drains Totaled A8L.
There are many solutions of cleaning the drains. The best is not to park the car under the trees, park outside when it rains hard for a long period of time.