Reply to problem with fader

so i've been having alot of problem with my deck a fader
if i move my fader all the way to the top on my s4 the fader on screen in traktor will slowly start to move down it also does this sometimes when i have the fader at the bottom but if i have the fader just a little bit off from the top or bottom its fine
i've sprayed some compressed air on it but its not working
any help would be great
thanks!