OK, extreme measures taken
The old watering can came out and I can categorically state that the fresh air boxes are very very very watertight, the washer spindles don't leak and the washer jets are also watertight
However, yesterday out in the rain, there was definitely water ingress from somewhere, resulting in water accummulating on the lip of the dash and then trickling down onto my leg. Same on the other side.
When I drove the notch down here last year, it rained then aswell but there were no water leaks. I do have a theory however.........
Having read the Haynes manual, it says, quote.........
"On the fascia, there are 3 levers.............the 2 outer levers control air to the screen independantly at each side. (so far so good
) The centre lever controls air to the footwell at the front fan behind the dashboard."
This second sentence is causing me problems because, despite searching high and low, I cannot find anything resembling a fan located under the dashboard, nevermind any ducting leading to it!!
Could it be that when the big lever is in the down position it is allowing spray to enter behind the dash because there is no ducting, where it settles on the lip and then trickles down?
I'm guessing here as I have never seen what is supposed to be there, but looking at the flaps in the open position, it seems my theory maybe plausible.
Over to the experts
