Just received mine today(3.5), it does'nt leak but I see the issue you mentioned. I order for me to keep that seal I try not to even handle the tank itself. The tip seems very snug so I screw onto the batt holding the drip tip. Also the flange has the sit in the bottom of the tank a certain way, a slight turn of the carto (holding the drip tip) will help seat the flange. Even if the flange is'nt snug my tank still does'nt leak though.
On another note; I love this thing. I watched the video again and it was like clockwork, no leaking, no mess and the hit and taste are great.(tons of vapor) I was able to get it to work with an (unmentionable) PT and USB wall charger, however it was'nt as good as with the King Diamond manual. I don't think I'll use it as a carry around but it's great when your just sitting around. Using Nuport Wow in it now. I see way Morandir likes it so much(great taste) may have to try 36mg jk. Great buy for the money