I don't think this is a thread-jack, but here goes.
My boat is a 1991 Prostar 190, freshwater only. Showing some rust stains at "leaking" down from the joint where the risers attach to the manifolds. 99% sure these are the original manifolds and risers.
Sounds like I need to at very least pull the risers and see how things look. I shouldn't be surprised if I need to replace 20+ year old risers/manifolds???