Pentax focusing ring stiffness

[Andre Langevin]

Yesterday I was using my K28/2 which is a rather stiff focusing lens 
and I noticed that the rubber on the focusing ring is a bit slippery, 
thus contributing to lack of ease when focusing.  Is there a 
treatment to give the rubber (it's probably not rubber actually, but 
some kind of vynil) its original "unslipperiness" that has worked for 
you?

Andre