most of the cheaper mixers on the market bleed after , in comparison, little abuse, as when you start, you tend to over apply pressure to the fader its slef, and the annoying thing is!! they usually bleed at the point where the fader actually hits the metal, not nessesarily where the actual cut off is!! as there is mabey a few mm where the cut off point lies!!
it will cracle, which is sometimes down to dust in the fader though!! so try anti static spay and lube!! (made for electical componants)
if the sound bleeds, sometimes on one side! close the fader and then lightly push it up/down!! it can be either l/r side or both thats playing up!!
if come up with a few temperary measures to deal with fader bleed in my time!! the best tip is, dont get a cheap mixer! i know its not the cheapest answer, but if its something you wish to keep, then its well worth saving up!!