Besides just installing new ones, is there a way to try and reduce slippage in open-geared tuners, such as on a guitar or mandolin? Screw driver? Talcum powder? Pumice? Mackintosh’s Toffee?
Try tightening the screw that holds the circular gear in position. If that doesn’t work, replace the tuners. They are inexpensive and easy to install.
read this, see if this speaks to you:
I have to opposite problem on my new Tenor Banjo, the pegs stick.