I don't think the Zelos kit is really prone to leaking. I've never had an issue with it. However, I fill to the fill line. Period. That gives you about 1.7 ml capacity (it's advertised as a 2 ml
tank). The only time I got a leak out of the Nautilus 2 was when an O-ring became deformed. It was my quitting
tank, and I subjected it to a fair amount of abuse. It's also a good idea to close off airholes when the mod is in transit, or when filling, etc. But, if used correctly, I would call the N2 the opposite of a leaker. My oldest N2 is close to a year old and my husband is now using all my N2s during his own, well, at this point I will call it dual use attempt. He also has had zero issues.
People who complain the N2 is a leaker are either overfilling it, using it incorrectly, or something has gone majorly wrong. I haven't seen a ton of folks state it's a leaker. Fiddly, annoying, lacking capacity topfill (after they've vaped a while) yes. Leaking, not so much. Also, it can be easy to flood the coil if not very attentive to the topfill process, so you may need to blow out any excess in the chimney prior to
vaping (blow gently through the airholes, with a napkin or whatever right below the airholes, to catch the liquid trapped in the chimney. Etc.)
But in my experience, it's been a total non leaker. I think I have four in my collection floating about.
I'd probably be just as inclined to recommend the Innoken Zenith tank for a good MTL vape, as well, although there is someone on the Zenith thread discussing leaking issues, although to me it sounded like a missing or defective O-ring, or a defective tank.
There is an O-ring under the top of the bell cap in the N2 that needs to be correctly placed, IIRC. I've had that O-ring shift or go missing, but any leaks were resolved by simply replacing it.
Anna