Reply to Problem with tempo fader

Recently my left tempo fader has started acting funny. When i move it the tempo takes ages to catch up with the movement. The screen shows the tempo counting through the bpms long after I have finished moving it. It makes using it impossible. The right fader on the other hand works perfectly, as snappy as ever. I thought it might be dust but I never leave the S4 uncovered and I have tried blowing into it a few times and recalibrating but nothing seems to work. Any ideas or does it need to go back?