Some fail in a few years, some seem to be near permanent. No doubt the longevity is as much to do with the system design as the actual part. And the system design can make the best elbow ruin your engine in a blink.

Friends have a stored boat right next to me. They have just had their system redesigned that included turning their elbow into a riser. They hydrolocked their Yanmar shortly after buying the boat. Then with the new riser design that had a brace on it, broke a fabricated SS pipe, so another brace was added.

They (their mechanics) think the hydrolock incident was caused by a back up through the exhaust. Their outlet is above the waterline and the exit fitting has a flap door. Before the new riser was installed(to get it well above the waterline and away from the engine), it had just an elbow off the exhaust manifold. But the raw water had a high vented loop. Not unusual to hear of hydrolocked engines in sailboats.

One of the best articles that I've used in my thinking is a Good Old Boat piece by the editor and Dave Gerr. It's been very helpful.