Don't know about the clamping magnets but simular magnets in pager
motors and other motors indoor flyers use have had that same issue.
They are formed rare earths with chrome overcoating and they all fail
in the same manner. The crome just flakes off and jams the motors. It
must be a manufacturing problem. If you posted pics and dimenslions we
all have lots of junked CD-ROM drives that we could send you a simular
part.
Richard