My pitch slider isn't functioning on my pioneer

Take off the slider from the main board and clean it with IPA solution, blow dry it take care not to scratch the carbon strip inside after that apply a very small speck of petroleum jelly or mechanism grease, used by technicians on the movable mechanical parts and you may get it working again. If you have the patience and the knack of doing it urself go ahead. If not order a new slider ( send the details correctly including the size and ohms rating) and replace it. After all pitch bending should not keep changing if you are a DJ so a new one would be most feasible in your case.