I have a clear Noodler Konrad rollerball. I was filling it one day, and the knob separated from the shaft. There are no threads in or on either piece. They appear to have been glued together.

My question is what is the best glue to use? I thought I read at one time to use rubber cement. I bought a small tube of super glue designed for non-porous surfaces and plastic. Should I use one of these glues or something else?