I replaced the sac on my Esterbook a little over a year ago. This week it started leaking, which was surprising because it had never leaked before. I pulled it apart today to have a look expecting to find a hole or tear in the sac. What I found was the sac had, for a lack of a better term, melted! It was just this really sticky blob of goo.

I have always been very good at cleaning the pen and have always used trusted FP ink. Mostly Noodlers Dark Matter.

Does anyone have any thoughts? Could it be the ink, or something else? I'd like to figure this out before changing the sac again.

Thanks in advance.