Good morning everyone! I've always used 'rubber' sacs. On one of my pens I have used a silicon sac which I'm now in the process of replacing hoping the pen will stop leaking. Asking around I've been told that silicon sacs are inert as they do not release toxic gases that can ruin old vintage pen bodies and so are to be preferred. 'rubber' sacs on the other hand release toxic gases that ruin vintage pens. I can't believe this. In the year 2000 we haven't found a way to produce non toxic rubber sacs? How long would it take for this toxic fumes to ruin a celluloid, ebonite or whatever pen, 10, 20, 50 years of continuous usage? Is this simply a myth? Are there studies out there that actually proof this? thank you. Marco