I finally got round to fixing my leaky boot. Mine was leaking through the rear window rubber ... here is what I did to fix it ...

Above pic: Lifted up the rubber seal where it meets the glass (the green lines show the area) and squirted silicon sealant into it, putting the silcon sealer nozzle deep under the rubber seal then gently pressed the rubber down onto the glass and wiped off the excess.

Above: The straight green line is where the water would run (on the underside of the metal - guessing because it slopes down a bit) and the green circles are where the water would drip down to.

Above: Lift up the corner rubber seal, insert silicon nozzle and squeeze silicon into here also.
Since doing this (March-ish?) the boot has been dry - *and it peed down this morning* and the boot is still dry so I declare problem solved.
Hopefully this will help others ...
Have fun ...