After hiking up the last cinder cone, my Black Diamond Contour hiking poles broke. Not the poles themselves, but a small flexible rubber/plastic ring that covers two recessed buttons to release the 2nd extension. The polymer degrades over time (UV exposure, outgassing, etc.) and it's normal that it would eventually crack and split.
I don't feel bad. They lasted over ten years. That's money well spent.
I visited REI last weekend to buy some replacements. I bought another pair of Black Diamonds, the model that most resembled my old poles. I got the Black Diamond Trail Ergo Cork poles. If all goes well, I'll get another ten years of use out of them.