I can see where O-Rings could cause flooding but not poor juice flow but thanks...Like @vapdivrr, I'd definitely say o-rings. I had the same problem with a K5. It took me ages to sort out and I'm a bit embarrassed to admit what the fix was, but making sure I lubed the o-rings on the base every time I rewicked has transformed a useless chunk of metal into a beautifully vapable tank.
I've since sorted out the issue. After watching Phil's video and a few others, I started trimming down my wick tails. It seems that I was tucking in too much cotton. The other thing I did was switch to wattage mode instead of temp mode. In temp mode the resistance just wasn't stable and I found the atty itself got very hot. Now in wattage mode, the atty stays cool and with the reduced cotton I have no wicking issues what so ever.
Another thing I did was to switch to the glass tank instead of the steel one so that I can monitor my juice levels. Once I get used to how much juice it uses I may switch back to the steel tank because my work day can be a little rough.
All in all, it's now the perfect vape that hasn't given me any troubles at all...