I put in a new windshield washer reservoir, the old one cracked. I sprayed the area behind the reservoir with a rust preventative after clearing out the fine debris that came down the drain under the cowl, l make a point of cleaning out the area under the cowl around the drain, but small stuff gets through. The drain outlet dumps the water into a pocket that has a drain hole but it was plugged with small debris. It makes a good spot for rust to start at. A poor design the end of the drain should be belowthe bottom of the car. I cleaned the same area out in 2011 when the fluid level indicator failed, I sprayed it with rust proofing at that time as well, no rust was evident.