Eye Dropper Filling and Grease

When filling a pen barrel directly with ink, the only place to put silicone grease is on the section threads, and maybe on the nib unit threads.  Avoid getting grease on the feed or your pen will not write at all.

Never put grease on the feed.

Use thick grease, like DANCO, which you can find online or at any home supply store like Lowe’s or Home Depot, maybe even Walmart.

I would NOT use the thin water grease that comes with a TWSBI pen.  That stuff is meant for piston seals, not sealing threads.