Do Lycoming sodium-filled valves rust from the inside out?

I just read an article on Bring A Trailer written by a fellow who owns a Citroen SM with a C114 engine. Interestingly, the C114 has sodium-filled valves.

Per the article, the valves are prone to rusting from the inside out if the engine is kept in a humid climate and used infrequently.

My knowledge of metallurgy is a tad limited, but I don’t understand how a sodium filled valve can rust from the inside out. Surely rust-causing water can’t have gotten into the valve during manufacturing or at a later time while sitting in a humid environment. A water/sodium reaction is quite energetic, and would likely destroy the valve abruptly rather than gradually. Possibly the sodium is reacting with one of the components of the valve steel, I suppose.

So I doubt the article’s author is correct, but I figured our experts here would know more about sodium-filled valves and the possibility of their rusting from the inside out. Can anyone shed some light on this?

I ground those vales back in the late 70's early 80's, machine shops quit doing them because if you nicked the stem they could create an unable to extinguish fire in house fire extinguishers were ABC's, water made it worse. Chips from machining machining porches/vw cases every where. Otherwise if care was taken, they should still be in service today. Mercedes Diesels engines had them also. just more valve face and different grind angles.

Never heard of internal rust on a Lycoming sodium filled valve. The stem will rust from sitting because of the iron in the guide.