Reply to 2 S4 problems

I've got a Traktor S4 a few months old (June 2011), It s works fine for regular gigging but I have 2 small issues that keep me from getting the full use of my S4

1. My input channel D isnt working so I can't use it with the Scratch upgrade or plug anything into that channel for that matter.

2. The Knob sensitivities are all different, not drastic, but you can notice there's different resistances for each knob. The main deck A and B knobs feel rough when I move them, compared to the C and D ones which feel just fine. I can still mix fine, but I believe this is seriously impacting my EQ handling and making my music sound not as good as it can.

What would be a good way to go about fixing these? The nearest store where i bought my S4 is 2 hours away. My last S4 went DOA after a week and they replaced it on the spot after a few tests. I'd really like to avoid downtime so what's the best solution, should I send it to Native Instruments, fix it myself or take it back to the store?