Had it on every metal cleat on the top cap of my PT185. Bought the boat from an owner in Houston, so it's seen salt water.
Sanded down and repainted the top cap, haven't reinstalled any cleats yet.
I only use the boat in fresh water.
There is the same corrosion under the paint on cleats on the transom.
Will it continue to spread if I don't repair it as I did the top cap?