Bravo III are notorious for dissolving like Alka-Seltzer. That is why the newer ones (2004 up?) have an additional zinc under the cavitation plate above the outer prop and a bullet zinc at the end of the prop shaft. Haven't heard of a recall, but there could have been one. Regardless, I've not seen any Bravo III that is left in the water hold up well. I would have the Mercathode checked out to ensure it is functioning properly and also make sure you using the correct zincs for the type of water the boat sits in. There is just a lot of dissimilar metal with a Bravo III drive and its twin stainless props so they are more prone to electrolysis.