Now the weather has turned colder, I've noticed that the rear offside window on our Mk4 mists up noticeably along the bottom, even after a run when the rest of the car is warm and all the other windows are clear. There doesn't seem to be any moisture getting in from the door seals as far as I can tell. I've checked the door drain holes from the outside and they seem OK.

Any ideas? I haven't taken the door panel off yet but I'm wondering if a damaged or missing vapour barrier might be to blame?

TIA Midge.