I owned a treadmill (second-hand, details long forgotten, sorry) which had two long steel rails (running the length of the machine) for the main structure. The

I owned a treadmill (second-hand, details long forgotten, sorry) which had two long steel rails (running the length of the machine) for the main structure. The brackets which connected the rails on the front side were steel, but the ones on the back of the machine were inexplicably plastic. There were major load paths (cyclical loading from running) going straight through these brackets to the feet. Between the wear and plastic embrittlement, these parts were the first to fail, and the entire rest of the machine was in decent condition (easily years of life left). There was nothing particularly complex about that part, they could have easily used steel brackets. I can't help but feel like it was designed for a specific lifespan.