I've got a wowboy carto here that I've filled up about 7 times already. It is still producing a good amount of vapor and taste but I'm getting somewhat of an oily film in my mouth. Do you think I over filled it last night, or is this just a case of you can only fill them so often before the quality declines? I figure 7 times is pretty good, I'm not complaining, just asking the people who know.