Thank you very much for your responce guys,
the keyb is a 10 year old Casio CTK-750.
I have opened it once or twice to clean the insides, but never went further than vacuuming the dust and cigarette ashes from the case, so I don't remember if the keys are the "closed type" you mention.
If so, it will probably speed up the replacement time, and a new one will take its place.
To be honest it is still very much usable, and I thought I just could slow down the wear a bit. If anything I will spray compressed air and see if it changes anything.
I will post my findings.