Not particularly scientific, mind you, but often works: 1) heat the refill slightly (NO flames, NO heat gun, some friction rolling it in your hands or a hair d

Not particularly scientific, mind you, but often works: 1) heat the refill slightly (NO flames, NO heat gun, some friction rolling it in your hands or a hair drier or run some hot water on it) you want around 40° or maybe 50° C, not more 2) try writing on your shoes (rubber) sole or on one of those largish rubber bands or even on the side of your car wheel (the idea is that there is more friction on rubber and the ball will start rotating again) Acetone and similar solvents risk to affect the plastics (if any) in case you want to try with a liquid (immerging just the tip in it for a few minutes), alcohol might do it.