A Darne is a gun that is cycled from open to closed, "briskly". I don't think there is much opportunity for wear in the case of this single design due to opening or closing.
If you ever witnessed how the guys at the factory handle them, you'd likely blanch. They are not gentle with them at all. After several lifetimes of use, they acquire a silky smoothness that is wonderful and easy to use.
I hate seeing people beat a barn hinge gun to death. I encourage them to try to do that with a Darne. They only get better.

Best,
Ted