I have seen a number of emails floating around about repairing A4 exhaust systems. Mine is both freshwater and seawater cooled. I just went through this repair saga. 'Recognized I had a problem only because my bilge pump was running more than ever before....leaking seawater. I have a '74 C&C in very good condition. An exhaust pipe had rusted through just below the 90 degree elbow where it comes down from the highest point (which prevents seawater back flow into the manifold.) I understand this is the MOST COMMON POINT where an A4 exhaust system will habitually rust through--part "I" of the diagram. Since my boat is very reliable, I decided to PERMANENTLY replace the entire exhaust system from the manifold on back with threaded brass components...rather than just band-aiding it with galvanized parts that might last 5-7 years. Yes, it cost a couple hundred beers for the parts, but my spare time is at a premium for recurrent maintenance, so I am now assured I will actually enjoy future spare time sailing, not replacing this again.
First, I obtained a new manifold flange from Don Moyer which is threaded for an 1 1/4" pipe. Second, The threaded brass components were obtained from www.plumbingfittingsdirect.com
who had the best selection of odds and ends and the cheapest price after shipping costs were taken into consideration. Third, I have attached a diagram of the brass components with a few configuration notes. Fourth, I removed and repainted the exhaust/intake manifold unit with high heat engine enamel while I was at it to spruce it up and preclude manifold corrosion. Fifth, you will notice I encased the brass pipes with a lot of high heat coating materials --high heat coating spray, heat shield matting, and insulating wrap--to minimize heat transference. This keeps the cockpit floor cool when the engine is running for extended periods of time.