Starting here.. anyway.. as I cut round I noticed a Foam behind the metal..
Yes that IS a form of expanding foam UP in the arch space to help deaden noise! How canny!
As you can see...
The part itself is in good order, has a slight bit of surface rust, but will clean up well...
Anyway, a little further back where the end is curved around the leading edge of the wheel arch, the two parts are doubled layers.. upon removing the end of the "Jamb", I discovered a GAP in the rear face...
Firstly, the square hole is the Citroen produced hole, NOT one I have made.. you can see theres a layer of seal that comes so far down then stops... below this where the two faces meet, theres a gap! This IS where the water gets through...
Removing a wheel, and peering behind the arch edge would reveal this behind any crap that may be sitting there..
Looking at the removed part, plus the "Foam" on the car you can then see where the water seeps across and sits..
So there we have it! The water gets in from behind the wheel arch leading edge!
Happy sealing and repairing!