Rain leaked into the boot of the estate over Christmas Now, it was parked at a funny angle in my Parents drive, but I'd rather not repeat as the carpet seems to have sucked up about 3 pints of water and is reluctant to give it up again I remember discussion about membranes in the boot door - I guess this at fault: the inside lining of the boot door was wet also. Presumably if I strip the liner off, then the membranes will become apparent? What's best to stick them back on with?
The membrane on estates is made out of much thicker plastic than usual, the mastic that was applied at the factory should still be pliable and may simply need manipulating into position. Alternatively I'd add some black windscreen sealing mastic, I believe Bostic make such a product.
Another place to look for leaks is around the wiper spindle.
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It is most likely the membrane. Leaks through the spindle hole will be caught by the membrane.
I had the same problem when I changed the rear viper-motor. After trying a few different products I ended up using Bathroom Silicone. The boot and carpet has been nice and dry since (Two years now). Remember to clean the mating surfaces before assembly. The catch could be that silicone may be a little harder to remove than the original stuff if you have to go back in at some point. I think the basic problem is that the membrane is made out of PE or PP-plastic and it is very has to get anything to stick securely to that!
I used a caravan sealer when i had this.Its a double sided waterproof mastic seal,in widths up to 33mm.I think i used 18mm,comes on a roll about 4 m long,about £4-8 depending on widths from any caravan or camping shop.I stuck the membrain on with this then ran a bead of sealer around the egdes to make sure.It never leaked again in the following 4 yrs i had the car.Was still dry as a bone when i sold it to steveG over a yr ago.
Checking the membrane is a good starting point, just remove the internal door cover. Watch out for hidden screws. If unstuck, silicone sealant is best, Dow Corning from a plumbers merchants is the best and cheapest.
Other points worth checking are the cable entry grommet at the top of the door and bodywork, the door seal on the bodywork for crushing or splits.
If the car is parked nose downhill, water collects under the seal and seeps into the car instead of draining through the bumper.
If you have a sunroof, check all the drain channels. The front two can be accessed with the roof open and rodded out. The rear ones exit into the rear wheelwells and get blocked at the ends. Pick out with a bit of wire.
Finally, drill new holes into the bottom of the boot door, but further out than the mislocated holes as supplied by the factory. Any water then collecting in the bootlid will exit easily.
Worth checking under the rear seatswabs as any water entering the boot can collect there. Use absorbent paper or newspaper to dry out.
Drying out the car is important as it will otherwise rot. I know I have a rotted one!
It's not raining or snowing here this morning (so it's -3 instead brrr) so I got the liner off. Membrane has indeed parted company with the boot door, and the liner is wet inside. Now fixed back on with no more nails and copious amounts of silicon sealant
On the down side, my fingers are frozen, and I measured the battery: 11.6V after standing only overnight. No wonder it's reluctant to turn over in the morning Off to GSF for a new un then!
Now, it was parked at a funny angle in my Parents drive, but I'd rather not repeat as the carpet seems to have sucked up about 3 pints of water and is reluctant to give it up again 
I remember discussion about membranes in the boot door - I guess this at fault: the inside lining of the boot door was wet also. Presumably if I strip the liner off, then the membranes will become apparent? What's best to stick them back on with?
Off to GSF for a new un then!