I went to use my Faber-Castell Essentio and it was dry. Only a little droplet of ink in the converter. I filled it on Dec 17th, so it definitely didn't make it 4 months. But I thought I just used it a couple weeks ago and it was fine. So maybe it's good for ~3 months max. Not a great seal. I'll add it to the case of pens that will be fine if I intend to use them a lot over a short term.
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