Here's the only possible solution I could find on the Internet. It's from a company that makes a concentrated cleaner called Pro-Tek:
- Artillery Fungus Cleaning - The black tar-like substance produced by the spores of this fungus have been giving East Coast homeowners trouble for years.
- We suggest a 20-1 ratio, tested in an inconspicuous area, and increasing ratio as necessary. (Never use full strength without testing)
Here is the link to their website: http://www.protekchemical.com/hints.htm#auto
The Delco Cleaning System's site states that pressure washers should not be used on painted aluminum surfaces and car paint because the finish can be damaged.