Funny you should ask. My wife and I have been trying all sorts of remedy's, which all required lots of elbow grease. Most of the remedy's such as Never Dull or Brasso are good at polishing brass, but not so good a removing heavy corrosion. We finally discovered what works good at removing the heavy corrosion - muriatic acid. Muriatic acid is also called hydrochloric acid. You can buy it by the galleon at hardware stores. It has may uses, such as cleaning bricks, swimming pools, cleaning toilets, etc.
Muriatic acid is an acid, so protect yourself by wearing rubber gloves and a face shield, and only use it out doors. Do not breath the fumes. You can pour this acid into water - slowly. But, do NOT pour water into the acid - you can get a violent eruption. We poured the acid in a small glass jar and used q-tips, dipped in acid, to clean the brass - works miracles. Make sure the acid does not drip onto the gel coat. Use a spray bottle with a 50/50 mixture of vinegar and water to neutralize and wash off the acid.
We have not found a coating for the brass yet that will keep it from corroding so quickly. I have been searching the internet and found a couple of possibilities, but have not tried them yet. I'll let you know what I find out.
