The problem with the bcc is heat. When the tank gets warm the air inside expands and pushes the liquid through the wick. Inverting does help. Also, I have found after vaping heavily, they collect condensation in the air tube and this can leak down through the coil into the battery when it sits for an extended time. This also seems to be part of the reason for the gurgling. I keep a few cotton swabs on me to push down in the hole to soak up the condensation ( I do this every time I refill too), then I remove the bcc and put a rubber cap on the mouthpiece and invert it if I'm not vaping it. Also when you release the power, draw a split second longer to empty the air tube of all vapor so it doesn't condensate as quick.
Hope this helps a little.
In all reality, this isn't exclusive to the bcc. The top coils do the same thing. Heavy vaping causes excessive condensation in the tip and goes right into the tube cause it has nowhere else to go. Matter of fact, my theory is that what most people
think is a leak into the battery area is really just discolored condensation - after all, it's the juice that's condensing.
Also, any time you try to rebuild or modify something that wasn't meant to be it's going to have problems unless you've gotten extremely good at it, which simply means you've screwed it up so many numerous times you have it all figured out. Obviously if the item wasn't of good quality to begin with this may not apply. But consider Kanger - one of the best fit and finish, for now. However if you try to anything but replace the replaceables, which is subject to speculation, or try to use somehting other than Kanger parts, it causes problems. Ergo - not a good idea to by a PT and then try to use a knockoff coil replacement from FastTech or elsewhere.
RBAs, RDAs, or what have you, are less prone to problems because they are designed so, hence them being a bit bulkier/substantial - they stand up better.
Another good note about 80% of whatevers out there - if they employ plastic parts, the quality will be less and the problems will be more. Plastic cannot be made as accurtely as metal or glass parts, it inherently can't hold tolerances very well.