5.7 manifold errosion

[Entourage]

You should replace the manifolds and risers every 2 to three years. You are asking for trouble by not replacing them. You cannot see the passage inside and could be rotted. If this rotts out while you are on the water or even out of the water with water in the manifolds it will end up going in your motor (cylinders) and will hydro lock, and you will have even bigger problems.