All of the Tokina 16-28 f/2.8 lenses had the same problem (AF/MF clutch), which is also a chronic problem on the similarly designed Tokina 11-16 f/2.8. Because they’re all failing for the same reason, we think it’s probably a real thing.
I’m always happier when I can find a logical explanation for the numbers. The Tokina lenses are a good example. They seem to have trouble with the AF-MF clutch system (if you haven’t shot with one, instead of an electrical switch or full-time manual focus, you move the focus ring forward or backward to engage manual focus). If we pull the rubber off of the focus ring, it becomes apparent the clutch is really two barrels held together by tape.
Tokina 11-16 f/2.8 with focusing rubber removed.
The lower (mount side) barrel pulls drops down once the tape is removed, showing the mechanical clutch. The teeth on the upper side engage the small collared screws in the internal focusing ring to manually focus when the clutch is pulled back to manually focus, disengage when it’s pushed forward.
Tokina 11-16 f/2.8, focus barrel separated
A lot of grit and dirt gets in there (probably from inside the lens) and sticks because there is lubricant on the teeth. The brass collars and screws break. So it makes sense that a heavily used lens, like a rental lens, might develop problems from wear-and-tear around the clutch.