I have 1 set of risers & manifolds from sierra that are one season old, and since I flush the motors every time,and dry berth, they are in excellent nick. I also have 2 pairs of what I'm told are the merc cast stainless risers, but need to check.
The other pair of manifolds are a bit older and whilst not leaking, they are the reason for the shiny new ones.
It'll all be for sale at some point soon but I haven't thought about the price yet.