You have to be careful when cleaning the keyboard plungers. There's a thin layer of conductive coating on them that wears off very easily with anything stronger than water and a tiny amount of soap. You can easilt rub it off as well if you're to persistent.
Might be possible to fix if you add some kind of conductive layer to them again, but it has to be very thin or else it might touch the membrane at all times. Electrically conductive glue perhaps?
