[jotzgr]

Look up any mid 90s Mercedes. They all used it. Or just search for "Mercedes secondary air valve". It is a metal valve instead of plastic. I just installed one on my 94 NG900 with 2.3 not a month ago, after my 2nd Saab one broke after I bumped it while trying to access the radiator drain. This is just an example:

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They are a fraction of the cost of a Saab one, if you can even find that. This one is high. I paid less than $20 for a brand new one incl. shipping. The hose ends are the exact same size as Saab. I had them send me the measurements before I ordered. The fact that it's metal, not plastic mean you will probably never have to replace it again. Just make sure the arrow on the valve points toward the engine when you install it (same marking as Saab). BTW, the same plastic valve was used on various Ferraris in late 90s, early 2000s, so you could search for that. BUT, because it says Ferrari, they are hundreds of $$.

 

[jotzgr]

Volvo also uses metal valves, and they still fail.

You are correct; any part can fail. On these, I've never had the valve operation actually fail. Because they're plastic, every one I've had ends up physically breaking, either at the nipple for the vacuum hose or the top of it (where it was originally glued together) actually blows off from the force of the air injection pump. Don't think you would encounter that on a metal one. I think this metal one is the 3rd one I've installed.