I've got evidence that my exhaust manifolds are starting to leak. I've been told I've been on borrowed time as the boats got 6 years of use in salt water. Anyways I've got some rust stains coming from were the risers bolt to the manifolds. I probably know the answer but i'm in denial because of the cost... do I have some time or does this need to be addressed immediately? Is there anything I need to be aware of before replacing these other than draining them before removal. Thanks in advance for the advice.