Recently, I've had two failures of the threading inside the pinch bolt of the left steering arm. The first failure came with no adjustment/fiddling by me - just natural steering and cycling on well maintained trails. The arm started to get loose such that it slipped around the steering bolt (king pin?). When I went to re-tighten the pinch bolt, I noticed it wouldn't cinch up and saw metal shavings coming out of the bolt hole. LBS replaced it with a brand-new-from-box steering arm and sent me off.
Second failure was when I went to adjust the arm after noticing that left and right were assymetrically positioned, and I wanted to re-position the left arm to match the right. Given the failure of the first arm, I consulted the manual on the adjustment before I worked on it. Loosened the cap bolt, loosened the pinch bolt, repositioned, lightly tightened the cap bolt, and went to tighten the pinch bolt down and it stripped again. I was only using hand-tight pressure with a hex key, and the manual didn't specify a specific torque number nor to tighten 'delicately', or 'lightly' as with the cap bolt.
My LBS took care of me and installed a new-from-box arm again (and the pressure he used was no greater than mine), but now I'm leery of making any adjustments to steering, lest I break it again. Has anybody else experienced this? Design flaw? Am I doing somethign to cause this in my riding, transporting, or maintaining?
Anything helps, as I would like to maintain my bike myself, but that particular part seems fragile?