Failed BMW Suspension Arm: destructive teardown

After changing the front lower arm on my E61 BMW 5 Series in the rain, I figured I should take something positive from the experience - so in the name of science I cut open the old ball joint to find out why it had failed. There's more than meets the eye when it comes to these essential suspension components; today we'll take a deep-dive into how they work and why they fail. This arm was an aftermarket item fitted less than 2 years ago - as I mention in the video, I wish I’d just changed the bush on the original BMW part as the ball joint itself was fine; only the bush was deteriorating (these are available separately).