I have a question regarding cleaning Koh-I-Noor Rapidiograph pens. I love the pens and think if taken care of properly they are worth the trouble. Unfortunately I have a couple of pens that the ink has dried up and I used the cleaning syringe and can't seem to resurrect it. If anyone knows of a tip or trick to revive them I would appreciate it. I hate to toss them because I neglect leaving ink inside them.