have cleared the little amount of leafs out of the drainage hole (not the problem)
if that thing ever gets blocked that is one hell of a blockage, the hole is huge!

know anywhere i can order one from at a reasonable price? local places and the dealer almost want 250 quid for just the front doors.

If it is the door seals, sometimes they can be brought back to life by a generous lube (repeated regularly) with some silicone spray. Rubber tends to shrink and harden slightly as it ages resulting in a less-than-perfect seal, and in your climate it would be even more so.

If it is the new windscreen it means it was incorrectly fitted or a poor quality non-OE part and you should go back to your insurance company. We had this with a Ford Focus where the installer didn't seal around the windscreen heater element wiring while installing and it leaked like a bugger. In your case it might be the bottom corner of the windscreen as this is a common place for leaks especially if the screen is a non-OE replacement probably due to subtle differences in the shape of the glass. Not sure if the seal "turning to dust" you mention between the dash and the body would be at fault - this sounds like it is inside the screen where water shouldn't be anyway.

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Cherry Rallye SOLD

Much appreciated i'll have another play around with it tomorrow, silicone spray and a re-ferb sounds like the plan,
since around the windscreen the outer seal is an inch short but to no effect,
i watched him install it, he did a very good job even though it has a maze of seals all around it.

i'll also put some small holes on the under side and top side of the seal since this seems to have been a common fix to this common problem.
since my driver side dosnt leak and it has chunks missing from the seal that must be a good fix