My '02 Jetta has been having a front fender rust issue for some time now. It is rusting at the top of the wheel for a different reason (another topic someday), but a couple of years back, rust started appearing at rear of the fender, at the rocker panel just ahead of the front door. Not much body rust anywhere else on the car which is good for a 17 year old car living outside in New York.
Well, earlier this year, the rust got so bad that the sheet metal just deteriorated and I saw dirt under the rust. I started digging and found about a baseball sized clod of dirt, rotted leaves, pine needles, etc inside the fender on both sides. Sorry, but I forgot to take any pics.
Fast forward a couple of months and I was thinking about where the "things" that fall in the space behind the hood, under the windshield wipers goes. Answer, it goes behind the fender!! Water probably just goes through the seams at the bottom between the plastic fender liners. But there isn't enough open space for solids to go through, so they clog the seam and just sits there, wet, causing rust.
So I decided to check behind the fender liner on my wife's '05 Suby, and this is what I found!
Luckily she doesn't have any rust-thru yet. When it gets warmer, I'm going to throughly wash out the area with a hose, and then treat with some rust preventative.
I don't know if this is common knowledge or not, but I have never done this cleaning before.
Maybe because I haven't kept cars as long as I do now.
Just my 2 cents.