Tektronix 2230 cal button problem

[nkurtar]

Hello,

I am trying to put the cal button back in its place. But can t fix it and get the cal button locked. There is a plastic shaft  arounf 2 inches long after the vertical knob removed. A kind of thin plastic shaft scares me to break it. Help me out. By the way cal button screw fixed type. But cal button turns freely even if i tightened  the screw.