Mine did the same on my current mk1, and my neighbours does on his mk2.
I sealed mine shut neatly with some silicone
I took the headlining out to see if any bolts/clips were loose too as water was running in like a tap! and low and behold, all 10 of them had about 3-7 threads showing! tightened them up (slicing hands open on the unfinished plastic) and so far so good, NO WATER!!!!
Did the above about 3 months ago.
Happy Winter Motoring FTW!
Adam