Originally Posted by charlie luciano

is the car RS or ST or have any type of tail gate spoiler fitted? As the RS spoiler leaks when the seals around the bolt holes to the tail gate wear out over time. Also rear light units are known for letting water in. Both these issues see water ingress into the boot. If you park the car uphill water could well be travelling into other areas of the car/cabin.

i had a mk2 transit connect which is basically a focus and it had a terrible water leak along the bulk head where a tacking device was fitted once, removed then holes not sealed properly, carpet had to be slung and new one off Ford on warranty fortunately. Maybe worth checking the bulk head area