sand?

More than likely it is years of debris that entered through the wiper arm vents and finnally settled into the lower core there. Trash and leaves usually do get down there. Sometimes holds moisture and causes rust. Just be sure to clean it out good and also check your heater unit making sure it is clean.

It's sand from a sandblaster.

hey andrew! andrew is the PO of my opel. do a photo gallery search for "jordan" to see more pics of my progress.