Our exhaust system
We've had only two problems with our exhaust system while cruising. One, in Puerto Rico where the 1 1/2-inch threaded pipe rusted through and blew off just as were leaving Boqueron for Salinas. We sailed the rest of the trip and found a local welder (charged us $10, but we gave him more).
The second problem happened in Trinidad just before leaving for Tobago. The stainless flexible pipe between the engine manifold and the muffler cracked and leaked exhaust. We learned that most good auto muffler shops can replace this pipe (we got lucky, only about $100 USD including cutting and welding).
Otherwise, check water and exhaust hoses and clamps regularly.