1970 swinger door lock

Which rod? The one from the lock cylinder to the latch? The lock cylinder end has just a "S" shaped end that goes into the hole on the tail piece of the lock cylinder. The other end has a small button on it that gets captured by a sliding clip on the latch. Slide the clip to the side, insert the linkage rod, and then slide the clip back to hold the rod. The questions is, why did it come loose? Something worn out or broken?