I've been reluctant to make an eyedropper pen so far because of the potential for leaks at the section/barrel threads.
Looking at the pen I got with a bottle of Noodler's ink, there's an o-ring that helps seal the joint -- but the only rings with about 8 to 9mm diameter that I've been able to find are much too thick for the purpose.
Do you think an o-ring is unnecessary?
Do you have a source for o-rings suitable for this application?
Thanks!