These boats originally had a 5 year hull warranty as stated. At 6 years G3 replaced one for me with a small crack. They sent me a new boat after I brought to a dealer asking how I could repair it. He called G3 and they sent me a new hull within two weeks I was shocked. They are a great company and stand behind their products. That being said it sounds like either saltwater or electrolysis on your hull. Plywood was used for many years on aluminum boats and I have never heard of an issue due to plywood treated or not. They quit using plywood due to weight and using a thicker aluminum and also made these rigs all welded. I would consult G3 on proper repair, they may offer help. Though, the boat is 13 years old almost three times the warranty period. Sorry to hear of your problem and hope it's a easy fix.