So I noticed the head on my M was pulling loose too easily, when I was trying to get the heat cap off between loads, so I went to adjust it, and already broke one of the tiny O rings that was on there. I scooted the other 2 down a rung, and it still fits in place, but it made me wish I had known to go ahead and just order extra O rings,none of the ones I have here will work. I thought it was similar in size to the O ring on some of my older ecig mouth pieces, but they were just a hair too thick, and wouldn't slide into the body with out stretching them. So now I am planning to try to find a reason to purchase another higher priced item so I can get some extra O rings with out having to pay $7 to ship just O rings. Hopefully I won't mess the others up in the mean time while I save up the funds for another purchase.
Maybe they should include a couple of spares, or suggest you order extras or something. Only having this for a day and already needing a part isn't the best feeling. I still absolutely LOVE this vape, just already running into a small problem. I don't plan to take the head off again unless I absolutely have to.
My advice: buy extra O rings with any of the modular units, to save extra shipping charges.