DDJ-s1 cross fader replacement

If you're in the USA: http://www.pacparts.com/part.cfm?part_no=DCV1023&mfg=Pioneer

Never tried to replace it, but I know that front-panel doesn't just pop open like a mixer, so it would require a bit of work to get it disassembled from the back. If you're not technically inclined, you may want to have a shop do that for you - you can contact Pioneer DJ technical support in your region to find a shop near you.