IIRC, that's a standard US made Schrader valve. (Looks like a tire valve core on steroids.) Try unscrewing the valve, photographing it and emailing the photo to a supplier to see if they can match it. Start with:

https://www.schraderinternational.co...c_lang=en-us-e

Thanks for the comments. I am unsure if this is a "standard" (i.e. car/bicycle tire) schrader valve. I looked at two L23's and there is no central "pin" in the middle. The central pin and spring is what holds a standard shrader valve shut as there is seldom much pressure on the other side. However, in this strut the pressure is 100's of pounds (3.3MPa = 460PSI) so the pressure itself holds the valve closed.

In the working L23 I can put a screw driver on the valve and unscrew the valve from the housing. On the broken L23 the valve just spins. My thinking is that the valve housing was stripped by someone applying too much mechanical pressure to it. So I believe I need the entire valve assembly (valve and housing) replaced.