There are actually two kinds of lock that are called "liner locks".
The older version can be seen on a lot of old Schrade (and, I assume, Schrade's sister brand Imperial) folding hunters, as well as more recent knives like the Case RussLocks. The Walker lock is a more modern design.
The old-style "liner lock" differes from the Walker lock in that the bent tab of the liner moves under the
bottom of the blade tang, usually not touching it; on the Walker lock, the tab wedges against the
rear of the blade tang.
On the old style lock, a slipjoint-type backspring holds the blade in place, and the lock is just a secondary safety block; whereas on the Walker design, the blade is held open by the lock alone.
The major flaw of the Walker lock is that it's susceptible to slipping, unless the geometry of the locking tab and blade tang are done just right. And since the lock is also the only thing holding the blade open, lock failure can be catastrophic to the user's fingers.
The old style liner lock, on the other hand, has a backspring that partially restrains the blade from closing on one's digits.
The old style line lock isn't as mechanically strong as the Walker lock; the stress on the locking tab is in a bending mode, rather than compression. (What's more, every one I've seen has been made of thin brass, not steel!) However, you could argue that it's more
secure, or more stable, than the Walker lock. On the Walker lock, the angled or radiused blade tang directs part of the force trying to close the blade into a sideways force on the locking liner, so that any slippage can cause the lock to fail completely; on the old style liner lock, there's no angle or wedge, nothing to push the lockign liner out of the way. The only way it can fail is gross structural failure of the liner.
As for our Original Poster: I'm sure there's no vertical blade play, despite your abuse; the backspring holds the blade tight, not the lock. However, I'd wager that the locking liner is at least somewhat bent. If I were you, I'd be careful about relying on that old, beat-up lock!
