The modified Platinum Preppy that comes with Noodler’s Waterase is equipped with an o-ring to prevent leaking of ink at the section. Pens converted to fill as “eyedropper pens” need an o-ring and/or silicon grease applied to the section. Usually I do not add silicone grease when an o-ring is in place. You may want apply some grease to your Waterase pens.

Platinum Preppy filled with Noodler's Waterase post silicone grease application
This morning I found that my two Waterase pens were leaking at the section. I store my pens nib up in a cup. This morning I left them laying flat as I was “up and down” from my desk to the whiteboard making a ton of notes.
Perhaps I had over-enthusiastically tightened the nib section to the barrel over-stressing the o-ring? With my non-Preppy eyedropper pens I don’t use an o-ring…only silicone grease. The Waterase modified Preppy comes with the o-ring which in theory should be enough to hold back the tide, er… ink. My highlighter eyedropper pen has never leaked with just an o-ring in place.
Anyhoo, I applied some silicone grease to the section thread and also left o-ring in place. All is well again. No leaking. Left them laying flat, too.
Silicone grease is more readily available to fountain pen eyedropper enthusiasts than it was even a year ago. Goulet Pens, Pendemonium, Writer’s Bloc, Richards Pens among others carry it. If you are buying Waterase for the first time, it wouldn’t hurt to add $2-$3 to your order for some silicone grease!
The caution about silicone grease, for those of you unfamiliar with it: use pure silicone grease with no additives. I found mine at Lowe’s in the plumber’s section. You can trust, however, that the fountain pen retailers listed above carry the real deal.
I will say that, uh, Waterase wiped clean off of every place it left a trail. Helps to have lots wood surfaces and no carpet! My fingers, however, need some serious InkNix-ing.
My original review Noodler’s Waterase Ink is here.