One note. Regardless of lack of care, 6 months is early for these kinds of problems. That is unless you were riding in salt/wet conditions. The screw should have been oiled or greased when attached, and the upper body is packed in grease which should have prevented any corrosion.

So, I'm wondering what this was subjected to which would account for this issue so soon. Unless you identify that, or at least have a theory, and make changes, there's no reason to believe that the next one will fare better.