When the marina commissioned my boat this spring they told me I had a leak under the exhaust manifold. It looked like just a loose hose clamp. When I went to tighten up the hose clamp the threaded part broke off the bottom water rail. Mercury has a bulletin out on this. The fact that they used a brass fitting on the cast aluminum water rail it was bound to happen. The over all condition of the water rail was good so I went ahead and fixed it. Spent a little time on the lathe making a heavy duty male aluminum bung. Cleaned up what was left of corroded fitting and prepped water rail to tig the fitting on to it.
