[phavriluk]

Is there a possibility that the connection between the tuner shaft and the tuner button has worn or fractured so that the button is spinning on the shaft? One screw is removed and all is revealed (don't lose the little washers and O-rings). Dirt-cheap fix if that's the case. And taking apart a good tuner will provide an example of what a healthy shaft looks like and a comparison can be made between the known-good shaft and the shaft on the failed tuner.

A trip to OP's favorite local luthier, assuming there's one that can be visited without packing a lunch, might also turn up a usable replacement tuner. Buttons can be swapped so that the eye isn't drawn to any mismatches. And factories aren't good sources for repair parts for anything, but repair folks are.