I had a similar internal water feature on my 54 plate Focus. If you open the boot and just prise down the rubber holding the roof lining up a little left of centre i.e. in line with where the pipe comes through to the boot, you will see where two pipes connect. Mine were disconnected so I just pushed them back together - job done. Water can show in the funniest of places and be nowhere near the origin of the leak! Good luck.