Concert C-30 sticky keys

[Altares]

Hello Korg nation!

My piano has some black keys that stay pushed and go back to their original position very slowly.. Is there a tutorial somewhere for repairing it myself?

I've seen a few on youtube but never about this particular keyboard. Can someone point me out to something close for reference?

Not willing to have everything dismantled and find out there's nothing like it to base my repairs on..

Thank you!