I see tons of people blindly recommend replacing manifolds every "x" years. If a person has a boat which is not stored in the water and flushes after each use 99% of the time the manifolds see fresh water. I live on the gulf coast and have manifolds last in excess of 12 years. Hey if you have the pre cat manifolds no big deal since they are cheap. If you have the catalyst manifolds, holy cow we are talking thousands of dollars....