Okay, I saw the caulking in one of the pictures. Had to go 10 pages back to find it though. I didn't notice anything when i replaced the O-Ring on mine.
After experimenting with different tanks last night, I'm actually kinda happy that the Danco O-Ring is so thick. Some of the tanks I had to screw all the way down to make contact. Any less thickness and I might have gotten a no atomizer warning.
All you guys that are ordering 2 and 3 iSticks, I'm wondering why you need so many. Unless you have a filling station at work, have one for just the car, and have one just for home. Carrying 2 of them would be a bit much, even for me, who carries an istick, ego twist, and 2 extra mini protanks.