This is a pretty simple repair, it just involves in replacing the potentiometer. However, the symptom is not a noisy pot, but rather a output volume that decreases by itself slowly.
The XPS-30 use digitally controlled output volume and the main potentiometer is just a voltage divider that feed into some auxiliary ADC. A capacitor is wired in parallel with the divided voltage to smooth out the operation. When the pot is broken and the wiper is not making contact with the tracks, the voltage on the capacitor slowly discharge through ADC input impedance, thus making the volume go down.
I replaced all rotary pots with ALPS ones.
