Hmm I'm curious what kind of juice are you using? Where did you get your 510 attys? I have some from thevaporpro.com and ecigsupply.com and both sets work well and have been working for over a month. Some things I have noticed about the 510... (you've been at this longer than I have so I don't doubt you may be in the know, but for what it's worth...)
I have to top off my carts OFTEN. It really sucks down the juice. I basically sit here with two 510s (usually different flavors), use one for a few min then let it sit in a cup battery side down, use the other for awhile, switch them... this seems to help the juice wick down to the atty between uses. When I've done that a few times and vapor/flavor starts dropping off, I refill my cart. I'm using PTB mod. I just set the cart on my desk and fill with several drops, wait a few secs for it to soak in, top off with a few more drops, then put it back on the atty and let it sit (battery side down) upright in the cup a few min.
So far this is the best way I have found to maximize the juice mileage.
I blow out/drain my attys nightly. About once a week I
clean and do a dry burn on all my attys.
The other thing is there have been a few juices that have NOT made my 510 attys very happy. Certain brands, or perhaps it has to do with the flavor/color of the juice? I have heard dark juices gunk up the attys faster. Higher VG content is gunkier too (but I like the vapor, so I don't mind).
Personally, I think the 510 is the best for TH and flavor (of what I have) but I do wish it were a little BETTER on juice mileage.

I'm getting ready to try cartos on a KR808D-1. We'll see...
Anyway, best of luck!!!