Disassembled the keyboard and removed all the keys and springs. This keyboard uses long strips of rubber membrane switches with conductive rubber pads on them. The switches are dual units with two contacts per key, this gives the keyboard velocity sensing, this works by timing the interval between the two elements of the switch making contact, the faster the key is pressed, the shorter the time interval etc.
All the rubber switches needed cleaning with isopropanol cleaner and then needed to be left to dry. After another hour in the sink with the individual keys, the next task was to repair the broken keys from the assortment of broken plastic parts that were rattling around in the case. All in all there was at least a whole octave of broken keys and all but two keys could be saved by gluing the broken pieces together.
I arranged the keys so that the top octave contained all the ‘suspect’ keys, this area is the least used part in my experience, so they would not get too much abuse up here.