DDJ SX Channel Fader Bleed

I bought my DDJ-SX second hand and when I got it home I noticed that the channel fader caps were a little loose. In order to get them to fit better I placed a really small cardboard shim inside the fader cap and press fit it onto the fader arm.

The issue I am having now is that the channel 1 fader bleeds unexpectedly at random times while i'm playing. I'm pretty sure it didn't do this when I first got it home and started playing with it but i'm now worried that I may have pressed too hard on the fader caps when fitting them to the arm.

Is it possible that too much downward force could cause the fader to bleed? Or is it more likely that the unit had a decent amount of use before I got hold of it and it needs a spray with some contact lubricant to give it some new life? Channel 1 was always significantly less smooth than the other channels so I guess it's possible that it could use some lubrication.

Any thoughts or ideas would be greatly appreciated!

Thanks