Hi folks and tech gurus, can you help...

I just picked up a used Numark DXM06. All functions work perfectly but before I paid the seller I knocked him down on the price and got it cheap as I noticed that the upfaders/channel faders do nothing whatsoever.

I can control the volume of each fader using the gain and the crossfader is perfect (no bleed or anything), the crossfader fades between the two channels, it's like the upfaders are stuck permanently 'on' (faded right up) but the volume doesnt reduce when I slide the faders up and down, it's like they are disconnected or something.
I've only tested the mixer using the line inputs but I could try the phono-ins with my decks.

I'm happy with the unit otherwise, I got it super cheap and all other functions work.
I can mix with it without the upfaders but it's not ideal

Could this be a failure on the digital circuit, dead upfaders (non-replaceable unfortunatley) or could the total failure of these faders be solved with a good clean and lube? The mixer was pretty dusty when I bought it, I just wonder if gunk and dust would totally stop the faders working in this way?

I opened the mixer today, cant see anything obvious that might be causing this (the faders appear to be actually attached for example but it difficult to the the connecters). The faders feel just as smooth as each other. I DID see two ribbon cables, a large wide one connecting the input section at the back of the mixer to the rear of the main circuit under the faceplate, and a second half-inch wide ribbon cable connecting to the bottom right of the main circuit board (near the front of mixer, close to the headphone socket area). THIS smaller ribbon is made up of about 10 wires, 5 of which appear pinched where it is trapped between the circuit board and inside of the body of the mixer where it all screws together. This pinching might be normal or could maybe be breaking an important wire or two that affects the upfaders. I just dont know.