It may be that the clearomizer tank has been overfilled. Remember, you only need enough liquid to cover the coil.
Please only fill the tanks from the bottom and do not remove the mouthpiece. Take care not to pour the liquid in the central column and not to cross-thread the tank and base when refitting.
Over time some e-liquids may break down the plastic tank and seals of your clearomizer. Avoid leaving e-liquids in a clearomizer that is not being used for a prolonged period of time.