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That's an interesting failure point. Only on the one section and only at the forward rotating part(or whatever it's called)
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That's a location of high stress intensity, or concentration, where the part transitions from the lug to the C shaped cross section.
There are signs of flange crippling before fracture. Crippling is a local buckling mode dependent on the cross section dimensions, and independent of the length of the flanges.
I would like to know whether the part is straight, or curved at the failure. Also note that the link above appears to be bent, possibly buckled. It's possible there was a single curve in the part for clearance, but not likely. The axial capability of the two parts, especially in compression, is not close. I'd need to see the geometry in the mechanism to understand how they relate.
There is a link in the idler where that part failed, so it's carrying a shear, bending moment, and axial load at the failure location.
If there is a reduction in depth of the cross section at the failure, that aggravates the condition.
I would look for a jam condition, and expect whatever caused it fell out.
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