Vintage tuner repair

[onewent]

These tuners are from the late 30s and have metal buttons.  I just noticed that one of them has a defective button, as you can see in the picture.  

Has anyone had success in repairing these?  Seems like the metal inside gave way allowing the button to spin over the shaft.  

It's a vintage guitar in near mind condition and I'd really like to keep the tuners.

Thx..Tom