Kurzweil PC3X Help!

Good day all,
 

 I just bought a used PC3X, and it suffers from a few problems:
 

 A- 3 of the MIDI sliders send random messages without touching them.
 

 I entered the 'Diagnostics Menu' via pressing keypads 4, 5 and 6. And the 3 affected sliders are showing random MIDI messages without moving them.
 

 I did a factory reset, but the problem still exists.
 

 Video: https://youtu.be/vVVy_-Oa5Qk https://youtu.be/vVVy_-Oa5Qk
 

 I contacted Kurzweil and they asked me to send it for repairs, but it's going to cost a lot.
 

 Any idea what's the type/model of the slider potentiometers used inside? And if I can replace them with sealed ones for better durability?
 

 B- There is a fairly annoying humming sound when I switch the keyboard on (probably coming from the power supply). It usually goes away in 15-30 mins? Any idea how to solve this?
 

 C- Some keys are very noisy and have a clicking sound (most probably the spring sound from what I can hear).
 

 Video: https://youtu.be/h5cQLpEWM4w https://youtu.be/h5cQLpEWM4w
 

 Thanks in advance everyone.
 Kay