I
recently had my van in the shop for a couple months over the winter
while I was taking care of some body work and other misc. maintenance. I
had a dent in the R side fender that I wanted to deal with and
that warranted taking off the fender panel. Wow, I'm glad I did!
This is what I found: 21 yrs of tree debris that had collected, composted and turned to soil in the bottom of this pile. This prompted me to take off the L side as well to see what was going on over there and clean things up.
Basically the same thing on this side. Remarkably there was no rust on either side, not on the bulkhead side, nor on the fender panel itself. Impressive primer job VW!After cleaning this up, fixing the dent and reassembling, what I did in terms of abatement of this problem was to run over to the local pet store and pick up a small block of foam used in an aquarium filtration system and I used this to plug the pathway on either end of the rain gutter underneath the windshield.
It's an experiment but I figure it will allow water to flow down and away and allow me to capture and clean out any accumulation rather than it accumulating and decomposing out of sight underneath the fender panel for the next bunch of years. 481k miles and counting ;-)