Audi A4 B5 Avant 1.9 (AFN) RHD, 1997, pre-facelift, 232,000 miles and proud of it. Magnificent machine. Mine for last 80,000 miles / 6 years. 5,000 miles oil and filter changes and she still runs like clockwork.

Hi everyone

Apologies in advance for what I know is yet another post on a much-covered topic, but I am stumped...

I've been lurking for a while, but this is my first request for help.
I have a front passenger footwell leak in heavy rain. It's definitely rainwater, not coolant.
Problem temporarily solved, sort-of, with duc tape, square funnel and receptacle to save electrics under carpet.

You can put a hose onto and around the cabin filter housing all day long and there's no leak inside. It starts dripping in once you move the hose about 1/3 of the way up the edge of the windscreen where it meets the A-pillar (passenger side obviously).

With the glovebox out, you can see where it is coming in - through a blanked-off square in the inner wing, immediately underneath the A-pillar.

The usual culprits suggested are either:

(1) blocked sunroof drains (mine doesn't have a sunroof)
or
(2) Water coming in from the seal around the pollen filter housing (I been over this with a fine toothed comb and a garden hose, removed and resealed the rubber seal around it, plus with the glove box out, you can see that it's not coming down through the blower, but dripping in from underneath the A pillar)
or
(3) Water coming in through the bonnet catch grommet (wrong side so can't be this)
or
(4) Overflow from blocked plenum chamber holes (I clear these periodically so it's not these)
or
(5) Defective front door rubbers (close inspection, they seem in very good condition, still flexible, as-new etc)
or
(6) Incorrectly fitted plastic scuttle panel above bulkhead (checked and re-checked...)

I have had the wing off and Tiger-sealed what I thought was degraded seam sealer on the inner wing from the outside - no improvement.
I have had a windscreen company test the windscreen with soapy water and compressed air - no leak there apparently.
I have put a smoke machine into the A-pillar from inside the passenger footwell but couldn't see any smoke working it's way to the outside of the car.

The only thing left I can think of is that there's a pinhole of rust underneath the bead of windscreen sealant that is letting water in. Before I pay to have the screen removed to check (and risk breakage of both windscreen and digital aerial), has anyone had any experience of any other causes of passenger footwell leaks not covered above that may be the cause?

Many thanks in advance for your help, and thanks for all the information on the forum. It is brilliant.
Also apologies to anyone that notices the duplication - I have started the same thread on a couple of the other Audi forums in the hope that someone will be able to solve this.
Best wishes
Niel