This thread has helped me immensely, so thank you peeps. Just signed up on VU just so I could post here for my first time. I got the Zeph a few days ago and love it so much I HAD to find a solution to the "seepage" that was happening on the bottom of the atty once I started using the RBA section. If I hadn't read reports from so many who were having no trouble at all once their build was correct, I wouldn't have been so excited to find a solution to my particular problem.
Anyway, as most of the important points are already covered by the rest of you, I will also stress that having all threaded connection tightened down completely is as important as proper build with this awesome atty.
The one thing I haven't seen mentioned here that may solve a LOT of problems is this: on the authentic, you'll notice the stock coil heads have a small clear silicone o-ring at the top of the bottom thread section. This would be why you might have zero seepage or leaking with the stock heads but still have problems with the RBA in use. Other than a proper build, check the bottom base of your RBA section threading - if there isn't one of those clear silicone o-rings like on the stock coil heads, there should be. Mine RBA head DID NOT have that ring in place at all. That ring is provided in the kit though, possibly as a replacement, and maybe because it's supposed to be actually on the RBA section and isn't, as in my case. Maybe the heads RBA heads are supposed to come with that ring installed and an extra one in the kit, but mine did not. So, I put it on there, screwed everything back in - and now no more seepage. Again, wicking issues can still let juice escape down those giant airholes on the deck, so I expect that from time to time. But not having that o-ring in place will ensure some juice loss and a seal issue.
And also - that is the same exact clear silicone 0-ring that is on the stock coil heads, so technically we DO have spares if we need them and primarily want to use the RBA head.
Hope this helps someone. And by the way I agree that maybe the only real design flaw with this tank is that the peek insulator at the bottom of the 510 pin channel should indeed been another mm or two longer down to the base of that 510 threaded channel to prevent any lateral movement with the pin that might result in a hard short. There may be a work around with that too, adding a tiny o-ring or something. But I will also say that when I got my Zeph, the stock 510 insulator down there was not fully seated as low as it should have been. It is now, and I've not had any shorting issues or leaking throuogh the 510 connection. Hope that helps too.