[courtartanis]

So, behind the (left side) lamp assembly there's water getting into the boot and running down the body and straight into the spare tyre well.
Interestingly enough, there's no water marks on the actual body inside, but I removed the trim panels from that side of the boot and chucked some water over the taillight and round the weather strip so it runs behind the light and it starts dripping through a black rubber gasket.

A previous owner obviously had the rear parking sensors fitted and whoever fitted them did a shit job, and just cut through the gasket to wire it up to the reverse light. Now I have no idea if they had water issues, or if the gasket has just shrunk or dried out enough to start letting water in, but that's the only place I can actually see it getting in.

See red line in the image to where the cut is and the reverse sensor wires pass through, and where the water is dripping from inside the boot.

Can I just fill the gasket from the outside with RTV?

[tw2005]

you could. I'd try and keep it to a minimum and try just sealing the cut area and go from there. bit of trial and error.

I had same issue and found mine with the whole body of that  boot torn apart from a trailer harness install.

silicone should work but if you want something a bit better or stronger, a  polyurethane sealant  like Sikaflex  or equivalent

example



Sealing mine stopped the wheel well filling with water

[courtartanis]

you could. I'd try and keep it to a minimum and try just sealing the cut area and go from there. bit of trial and error.

I had same issue and found mine with the whole body of that  boot torn apart from a trailer harness install.

silicone should work but if you want something a bit better or stronger, a  polyurethane sealant  like Sikaflex  or equivalent

example

snip

Sealing mine stopped the wheel well filling with water

Cheers, will give it a go 

[PhireSideZA]

Just chiming in here to say I had the same issue which was caused by the wiring for the tow hitch being routed incorrectly.

One day after a rainstorm I took my car out and at the first stop street I heard water splashing behind me onto the carpet where my feet go

The water dammed up in the wheel well, then the momentum of the water rushed forward, underneath the seats and into the body of the vehicle itself all around my footwells.

Took me a good day to use silicone to seal up the holes where the cables were routed (right side taillight) and dry up the water with a bicarbonate of soda and vinegar scrub to get the putrid water smell out of my interior carpets. I was not impressed

[courtartanis]

Just chiming in here to say I had the same issue which was caused by the wiring for the tow hitch being routed incorrectly.

One day after a rainstorm I took my car out and at the first stop street I heard water splashing behind me onto the carpet where my feet go

The water dammed up in the wheel well, then the momentum of the water rushed forward, underneath the seats and into the body of the vehicle itself all around my footwells.

Took me a good day to use silicone to seal up the holes where the cables were routed (right side taillight) and dry up the water with a bicarbonate of soda and vinegar scrub to get the putrid water smell out of my interior carpets. I was not impressed

Seems to be a common thing then! People cutting through those gaskets with reckless abandon.
Was it the same thing? That black rubber boot?

Mine wasn't quite so bad, although it was amazing how much water gathers from a small cut. My spare tyre was almost submerged and it wasn't until I went to change a turn signal bulb that I noticed a little wet patch on the carpet and the pond underneath!

[PhireSideZA]

I'm speaking from a very vague memory here, but I seem to think that my car had a gap for a spare harness that was unused. For some reason they decided to cram all the wiring through the smallest hole that there was and that caused some damage to the rubber gasket