Autocord metal embrittlement

As you can see, my focus lever is in perfect condition. However, I've learnt that the stamped sheet metal the focus knob is attached to is made from an alloy that became brittle over time, and that this is the reason so many focus knobs have broken off on the autocords. I'm very careful with mine.

Do any of you know what kind of alloy this is? Do you know the reason for the embrittlement?