I had a pair on my old V6. They'll outlast the engine, as long as you don't run them dry.
Mec ran them for a few years and then stopped making them. The story I was told was that they were replacing so many under warranty (because people were running them dry!) that it was un-economical for them. Shame really, they solve the problem of having to replace elbows every few years...
Why would one run dry? Thats just asking for a water impellar change. Unless your talking about dry exhaust. BTW, what exactly happens when you run them dry?
SS and cast iron expand and contract at different rates. During an oveheat, the gasket between the SS riser and the Cast Iron manifold fails and you get water in the cylinders when you shut the engine off.
In salt water, that is a recipt for disaster if the water sets in the cylinders for a couple of days.
Would it be normal for SS risers to have a thin film of rust around the hose connections and inside the jackets if used in brackish waters? The fittings, especially the little hose fitting are all as meaty as new though. How could one definitely tell them apart from low hour cast iron??