This 1999 Bravo III outdrive is suffering galvanic corrosion from operating with aluminum anodes in freshwater. The prescription:
1) Exposed areas on the Bravo III's aluminum housing need to be scraped, cleaned, primed, and re-painted;
2) Replace aluminum anodes with magnesium anodes;
3) Install magnesium propeller nut anode.
Photo courtesy of Tim Tise
All rights reserved. Used with permission.