This 1999 Bravo 3 outdrive is suffering galvanic corrosion from
operating in freshwater. The prescription:

1) Exposed areas on the Bravo 3'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