Inca dust ingress

Our 2007 Inca EK has a moulded plastic panel fixed to the ceiling, just behind the Luton. It's just decorative, holds a light fitting and hides some wiring and the underside of the fibreglass roof.
Recently, we have noticed black streaks coming from the edges of this panel, looking like black dust.
Removed the panel, absolutely filthy up there, and with a bit of a draught. Best guess is road dust is being blown in through some aperture as we drive along.
I would have thought that if air can get in, presumably so can water, although everything up there is bone dry, with no evidence of previous damp. However, we have had a water ingress previously, which we were told was coming from the awning rail, and was fixed.
The slight draught I can feel does come from the awning side, so I was wondering if the two could be connected.
Anyone had a similar issue, either with Incas or similar vans of the same time - I think Nuevo and Sigma might be candidates?

I should have said the previous water leak manifested itself on the nearside panel about half way down, in front of the window. I.e. nowhere near this dust issue.

Peter Brown wrote:I'm guessing someone took out the 400 x 400 roof vent in the Luton - any chance of a photo and ideally of the outside of the roof as well?

Peter

Ahhh! I think I may be about to feel a little foolish.
The roof vent is still there, but it makes a hell of a racket over about 40mph.
Soooo, I stuff a cushion in it - cures the noise problem but is that leading to this black dust problem?

Sorry, can't do photos at the moment.

Still can't do photos. Have cleaned everything up and replaced it, but can someone tell me if I must not block off the roof vent while travelling.
It's quite serious, because with it unblocked, the noise is intolerable. It's probably enough to make me change van.
Thanks,

Many thanks Peter.