Tk-fine vario repair help

https://preview.redd.it/tnl3mek9uq4e1.jpg?width=3024&format=pjpg&auto=webp&s=8afa4e581493425442196a666f1fb684a0ea1614

Hey guys, I've been using my Faber Castell Tk-fine vario for a while, and the metallic part started to get rusty, I guess. Has anyone had this issue before? If so, how can I fix it? I need your help!