My Leonardo Momento Zero seems to be leaking ink. I think it's coming out at the base of the nib unit/section interface and I think it started after I swapped nib units to try some different nibs. I'm wondering if there is supposed to be an o-ring or something on the nib unit, because there isn't one on mine and maybe I lost it during the swap. Is there? Anything else I should look at?

Thanks!