Here I show how to remove the keys from the keyboard of a Korg Poly-61 and how to attach them again. This procedure should be the same for some other Korg synths from the same era, e.g the Polysix. The keys in this one were really dirty, especially on the underside so I washed them of in the sink before attaching them again. I also wiped off the metal frame on which the keys sits as there was quite a dirt buildup there.
Do not lose the springs! 
Nasty stuff under the keyboard 
All of the keys were covered in some grey/black dirt 
All of the keys cleaned with some dish soap. Sorted to make assembly easier
