The leakage could be caused by a few different things but is fairly common with RDAs. The first, and most common cause in my experience, is over dripping. If your cotton (or whatever you use to wick) is already completely saturated it will be unable to hold additional liquid and this excess liquid will often leak out of the airflow holes. The second possible cause is if you exhale through your RDA prior to inhaling. This is done by many people in order to keep the vapor cool and "fresh" while giving your coils a chance to heat up. Despite the effectiveness of this technique if there is any excess liquid in the RDA it can and will be blown out of the air holes in an amount proportional to the amount of excess liquid, strength of the exhale, and amount of air flow. The last possible cause that I will mention is your wicking technique. For example, if you use organic Japanese sheet cotton the outer layers on the sheet are made of compressed cotton which does not accept or hold juice as well as the inner, fluffier layers. That's not to say that you should not use the outer layers, rather I have found it effective to cut with and not against the grain of the cotton and then ensure that the compressed layers are on the sides of the coils and not the top and bottom. This will allow you to drip directly onto the cotton from above without worrying about the juice flowing along the grain of the cotton, absorbed, and settling at the bottom of the RDA leading to a small pool of excess Juice. Once you have identified the particular problem it should be fairly easy to correct. Please let me know if you have any additional questions or problems; good luck!
