Hi Dave,
The drains are not the problem in my case. The leak is external rain water (or when washing car) getting in somewhere high up under the dash board.
The water runs down and drips onto the area next to the handbrake.
I think it must be around the bulkhead/wipers/screen area where it is coming in.
In heavy rain, it has shorted across some electrics and my indicators come on with no control to switch them off until the rain stops.
Regards
Mark
