Well I've had a look on google seems there could quite a few reasons, I've done the rear light, there's seems that there's no grommets out of place, so it was out with the spare wheel and the side carpet and I got the hose out.
I notice water coming in from some sort of vent that sits behind the bumper, so back out with the sealant, hopefully it will sort it. ![Smiley :smiley:](https://www.mk5golfgti.co.uk/forum/Smileys/newsmileys/smiley.gif)
I had the very same problem, traced it to the drivers side rear quarter body vent.
Removed rear bumper, removed vent, initially, I applied a bead of silicone grease, worked for while then still let some water in. In the end got a new vent, comes complete with new seal, I coated this with silicone grease, to try and give it some protection.
Silly Germans used a seal that absorbes water
![stupid :stupid:](https://www.mk5golfgti.co.uk/forum/Smileys/newsmileys/stupid.gif)
so over time it perishes and fails.
Did the other side also. Got the hose pipe out then drenched the area in water.
![happy2 :happy2:](https://www.mk5golfgti.co.uk/forum/Smileys/newsmileys/happy2.gif)
Regards.