rear nearside pillar water leak

Yet more problems with my RR. After finding the DVD sat nav filling with water I took the rear inner plastic from the nearside rear pillar to discover water leaking down from a weld/joint near the ceiling liner. I have replaced the boot rubber, but made no difference. How is water getting into and behind this joint? Could it be the tailgate hinges are leaking? The joint doesn't even look particularly well sealed. I need to sort this before replacing the repaired sat nav, many thanks

The official Land Rover cure was a plastic bag over the equipment

It is possible the hinge mounts are leaking and a good going over with sealant probably wouldn't hurt.

It has also been mooted that another possible cause is the folded join where the roof panels are joined to the 'C' pillars. Water works its way through the folds by capillary action and runs down the C pillar into the electronics bay.

I have the very same problem, I fitted a new tail gate seal, and still have the same p[problem, my water would appear to track down the inside of the corner pillar, and appears in the boot behind the rear bumper. I have concluded after many hours of frustration and wetting different areas of my vehicle, that it must be the seam in the body work to the side of the upper tail gate hinge, where the different panels are joined.
It is my intention to remove the upper tail gate, to gain proper access and then completely re seal in the affected area.

Many Thanks,
Mike