Just to add more info if I park facing up a slight incline water drips out of both rear ends of the sill. likewise if i park facing downhill it drips from both front ends of the sill. We had heavy rain last night and at 12.30 today it was still dripping. I've checked the drain holes and mesh both sides of the plenum chamber and they are clear. The bit that threw me originally was that i had parked at an angle facing down hill hence just one corner dripping .Ive made a booking with BMW dealer for next week but when speaking to them it was only a reservations guy who said he had made a couple of similar bookings but didn't know the outcome. it may be ok but seems a lot of water is held there.yes,,it's just the water drainage channel,but also check the drain mesh coverings,,sometimes block up with debris..
The front dripping is normal and just from the scuttle drains. They do have a habit of blocking and need cleaning every now and then. There is also an issue with the rear quarter panels filling with water which is well documented on here and is more of an issue unfortunately. Normally you will here water swooshing about if the quarters are full.