I have three Opus 88 Picnics -- I love the fill system, but two have given me lots of trouble. The green and blue models just stop writing suddenly and the nice folks at Opus sent me new pens. I just swapped in the new nib and feed on one and the writing is better, although there is the occasional need to bang the nib on a pad of paper.
Today I got my second replacement pen, unscrewed the new nib and an o-ring came flinging out. I'm not sure where it's supposed to go. There's one on the neck and I presume one fits somewhere below. Does anyone have any idea how to re-insert it?
Will try the new pens with more lubricating ink. The Good Goulet people suggested Noodler's eel inks.