I put a little silicone grease on the collar of the nib unit to keep ink out of the section. Any grease that gets squished out is wiped away with a napkin or q tip.
If you have a super thin o ring that fits here without making the nib unit too difficult to remove later, that works too (let me know what you’re using if so).
I don’t know if I full understand this and wondered if you could do a video of it