Comment by lazide

In both cases, the real issue is when the oil (eventually all do) oxidizes and ‘gums’. Tight tolerances make it cause worse problems sooner of course, but it’s the same problem eventually.

Putting new fresh oil in it often temporarily fixes it because it dissolves some (or a lot) of the old varnish. Acetone can often do the same thing too, but can also wash the varnish deeper into the mechanism where it turns into really solid ‘plastic’ when the acetone dissolves.