I noticed my ladder had quite a bit of wiggle as I climbed up. It looks like there is a shaft that should be inside - completely missing. The rail on the other side of the ladder has one. I plan to get a 3" piece of aluminum pipe (heck maybe PVC would do the job as it really wouldn't bear any load), drill a hole, and run a screw.
Maybe just a heads up - inspect your ladder. This is about 8' up between the 2 pieces of the upper ladder, high enough to get hurt pretty bad.