Inside the barrel of a Montblanc ballpoint sits a narrow, tapering tube which in normal condition is firmly attached to the front cone, that is to the writing tip. It can only be removed towards the threaded end of the barrel. If the tip breaks off, the tube loses its anchorage and protrudes from the lower end of the barrel. The sight is unfamiliar, but it follows from the way the pen is built and is no mark of a fake in itself.
The authenticity of a pen can be neither proved nor disproved by this component; what should be drawn on instead is the execution of the star, the clip, the engravings and the general finish. For a repair the only option is the manufacturer's own service, since Montblanc does not release sections or other spare parts to third parties.