Stiff focusing ring

[Orio]

I have noticed that if you leave a lens with stiff focusing ring, near a warm place (not hot, just warm), like a portable hard disk, after a while it becomes very easy to focus. Unfortunately, back to ambient temperature, it becomes stiff again.
I think that a chemical alteration to the grease happened, in the stiff lenses, that raised the temperature point at which the grease becomes fluid.

[Attila]

Yes, this effect is a real danger at summer time for blades.