Sorry to see that damage.
I hope this gets fixed for you soon. I haven't seen that kind of breakage before.
Definitely Odd, But...
... it's an older watch and I doubt the manufacturer will fix it for free.
They should fix it for free....
Unless something dramatic happened - like the watch fell to a concrete floor from 6 feet (or something like that) - Zenith should fix this for free. Inform them that a steel chronograph part like that should never break simply from normal use. I once had ...
You can see the marks on the other component that that part slides over.
Something wasn’t right regarding the clearance, and over time, with usage, it’s suffered material fatigue. There’ll be a fair bit of material debris in there, and it’ll accelerate wear on pivots, etc – so don’t even be tempted to continue wearing it. ...