First of all I had a right game getting the sideskirt off the car because someone in the past (not original) had bonded it on as well as the original fixings. We'll come to that later...
Anyway, here's the nasties: WARNING: This is not pretty!




So in discussion with me and my welder, the bonding on the sideskirt lip onto the edge of the sill on the car has meant that the water has had no route to escape and remained trapped underneath.
Which kinda of explains why the passenger sill is nowhere near this bad - because it's not bonded in place! So it's getting new sill and rear wheel arch panels welded in and then off to a bodyshop to be sprayed up.... rather sooner than I expected but hey.
Let this be a warning for those of you fitting kits in the near future!