Reply to Kontrol S4 problems

Hi, I've been having troubles with my kontrol s4. The Deck A and C faders don't always fade out completely when they are pushed all the way down, both jog wheels push functionality does not work properly, one of the effects buttons doesn't work and pretty much all of my knobs are loose. I bought the system used so I guess this is what I asked for but are there places that people can believe of that can replace what is broken on my system? Would NI even do these repairs outside of warranty? Thanks for the replies!