I just found your post. I also had same problem with 2. I could bubbles moving so knew stick still good. After trying many things I GOT IT!!!!!!!!Heres what I did:
pull cartridge with tip still on out of stick. You'll see a small gap at base of white part of top of cartridge. Pry that off. I took a pin and put in whole. A bit of glue had dried up. Not hard but sticky/gooey. I swirled pin around and got out bad glue. Put back together. lightly tap tip of pen on paper. If you slighty lift you should feel, I also heard, the ball going in and out as ever so slightly lifted off paper. hold pen to paper and glue should slightly start flowing. move slowly on paper and glue began to flow.
I am going to try storing with tip up versus down which is what I was doing.
I have tried and forgotten numerous times over years to get flowing and refused to throw out. I am glad i didn't. Even though we are talking about less that $10 this fix is so worth it made my day. Had to post this as my frustration versus many other peoples I hope I made others day. ENJOY!!!!