You can also put some pencil graphite in a bag, smash it till it's a fine powder, and coat the sac with that.
It won't hurt your pen....
110% satisfaction guaranteed.
Or get a tube of powdered graphite at the hardware store; it's often used to lubricate lock mechanisms.
What will the graphite do to the sac?
Edited by pajaro, 17 August 2017 - 00:06.