Some put a hole in to loose water out .Just put a bit of sealer on it .But that is not your problem . Check the seal on the rear wing around the electric radio mast and the other half in the boot . The mast will have a drain hole in it at the bottom ,and sould have a little bag in there held on with a rubber band to catch water that comes down the mast itself ....And as before the rear lights can and will let water in if they are not sealed up . They have been in there a long time ,,so the sealant is cracked ,, and doing nothing now . Pull the rear cluster out and re seal it .I used silicon grease on my seals every few years i check them . Not forgeting the rear window seals they can leak in to the boot eventualy. The saloon has this rust trap in the boot .As you lift the boot lid look in each corner of the boot gutter .The shape of it is wrong all the rain lies in there after a rain fall .I catched mine just in time it had started to rust,, but i soon stopped it .And its the first place i clean out after a rain fall .
