My keyboard Yamaha S08 suffered from several "sticky keys" disease already a year, perhaps more. That saying, I am pretty bad piano player. However, I like to have my devices fully functional for any cases.
I have found a very helpful guide, but with no photos. I made some for better visualization of the repair.
First, I unfastened all screws from both sides:
Second, I unfastened all screws from a wooden base plate which were holding the part with electronics.
Then I unfastened the golden screws holding the whole keyboard to the wood. The keyboard was now accessible from both sides.
The last step is described in the following video. It was just removing the sticky keys and reinserting them without a metal spring coming inside. The end of the metal spring has been left outside of the key:
So far it works well!