I actually can probably help you out on this.
I had the same problem on my Hatch, and worked out how to fix it. The person before me had tried running silicon over parts of the seal it didn't work.
The way the water runs down the hatch, is on the inside just outside the seals of hatch. It then actually runs infront of your taillights. (between the lights and the body). You should be able to notice a small gap there. Take your taillight off, and remove the seal.
Check the seal, and if possible try using silicon around it aswell, or just go out and buy a new seal. I brought a new seal, and light because my old light had gone mouldy
. After i did that it hasn't leaked again.
Hopefully his works for you.
sarujin