u/CharmingLeague7160

I inherited this Montblanc Mesierstuck classic ballpoint a few years ago, I however cannot use it as any slight preassure on the nib when extended causes the rotatable back portion to pop off, I think there might be a problem with the internal mechanism (black and yellow parts with the brass housing). I also do not really understand what normally holds the pen toghether. There are no authorized Montblanc retailers near me that can look at it and sending it in feels like a big steo wehn I don't know the severity of the issue, any help or information is appreciated!