I solved the problem.
On every plastic case I have ever seen, the parts of the case fit together
without any circuit components.
The case with the WD Media Stick is the circuit board fits between the two
halves of the case so that there is basically a sandwich with the circuit
board as the filling. The edges of the circuit board are visible between
the two pieces of the case and the two case pieces do not fit together.
This design exposes the circuit board to outside effects such as dirt,
moisture, static electricity and heat.
I have been working with electronic devices for sixty years and I have
never seen a case for an electronic device made this way. The electronic
circuit should be completely inside and protected by the case and not an
exposed part of the case.