As you use the liner lock, the face of the liner wears (gets shorter), and it begins to march across the back of the blade tang. Because the blade tang is angled, the lock-up stays tight. At the very end of its life, the liner will reach all the way to the opposite handle. Now remember, the lockup stays tight because the stop pin and the liner combine to keep the blade from moving, when in the locked position. So, once the liner reaches the far handle, as soon as it wears just a little bit more, it will no longer quite reach the blade tang. That means your knife will start to develop a wobble in lockup. Worse yet, now much of the time when you put force on the spine, it will function like an impulse force (because the blade travels to meet the liner), and liner locks are susceptible to impulse failures. And, sometimes the liner slips all the way between the blade and the far handle, in which case, it's just useless.
Phew! Still with me? Anyway, the answer is resoundingly "yes, liner locks do wear, and have a life". However, it is possible to bring liner locks back from the dead! Again, if you think about it, it will be obvious: if you insert a very slightly larger stop pin, the tang of knife will stick further into the blade handle. When that happens, even a worn (and thus, short) liner can reach the blade tang again. In fact, by doing this, you can get the liner to start all the way over on the left side again, to start the wear cycle over completely.
Joe
