Beside the coils not seating properly this is the list I look at, some juice specific, others climate and environment specific
1) Everything seated and sealing properly
2) RBA Specific - adequate wicking to keep liquid from flowing in by gravity and usual pressure alone
3) Juice Specific - Liquid mixture blend (a 70pg 30vg liquid will seep in easier than a 30pg 70vg liquid will)
4) Climate Specific - liquid viscosity will be affected by temperature variables (warmer the outside air is, the thinner a liquid will become, colder the thicker it will become) - remedy store tank upside down when moving between two different temperature environments, or hold upside down, open the tank and let pressure equalize
5) Climate Specific - liquid pressure and air pressure due to temperature will rise and fall, move from an 75Farenheit environment to a 100Farenheit environment, pressure will increase with the liquid and air in a tank building, this pressure will push liquid out - remedy see #4
6) Environment Specific - Increases and decreases in altitude can cause a fall in pressure in a tank (causing negative pressure) causing a pull of liquid into the airflow path to equalize pressure, and in reverse and decrease in altitude builds pressure in a tank similar to #5 - remedy see #4 store the tank upside down to where only air is allowed to be pulled or escape
Coil aging attributors to leaking
Wicking getting clogged or deteriorating due to these
1) Age of coil, older the coil head is the easier it is to leak due to wicking clogging and not letting liquid to be vaporized thoroughly, these cloggings can be carbon build up on the wire, crystalized sweetners, impurities in the liquid which do no vaporize creating gunk on the coil and wicking.
1A) Highly sweet liquids - savory, custards, candies, some overly sweet fruits, bakery liquids fall prey to this
1B) Darker Liquids - the impurities and colorings of these liquids do not vaporize and clog up wicking, coffees, tobacco flavors and such fall prey to this
1C) Tobaccos, including Whole Tobacco Alkaloids (WTA) and Naturally Extracted Tobacco Alkaloid (NET) liquids fall prey to this, particulates of the extraction and colorings clog up wicking
1D) Thicker the liquid is (higher VG) will clog up like Sweeteners in liquids will as VG is generally sweet by nature depending on what it is extracted from, examples Palm extracted VG is really one of the sweeter VG out there, also because VG is thicker than PG it takes more work to wick so wicks slowly leading to potential wick scorching and dry hits
1E) Power output - higher the heat applied will wear out wicking and wire quicker than lower power output, opening up potential scorching of wick and wire
hth.