My lathe was stored for a few years, after which the collets were partly rusted. These were stored in a wooden plate with holes, which apparently had passed on some moisture.
Contrary to the fear that the collets would have to go to the scrap box, they could be saved quite easily by carefully filing the rust off radially with a fine file (a bit out of focus in the background).
Then the collet looks like this. A discoloration remains, but you can no longer feel any unevenness. According to the clock, the concentricity is about 1/100. The machine is a Leinen DLZ 140.
It may not always work that way, depending on where the rust goes and the quality of the material.