At sticking keys the so-called gilded feather contacts are filthy. The best solution is not to clean but to twist the feathers. Per key, each consonance has a gulded feather. In the upper manual there are 5 feathers per key, in the lower 3.
To reach the feathers, the upper metal frame must be put upside (check register and pedal contacts). With that the keys become well visible.
Next, unscrew the 2 propellers at the outside of the cupboard (NB the capsules are provide with propeller wire). By unscrewing the 2 frame-screws at the inside of the cupboard, the frame completely overturns with the keyboards down.
At the upper side of the electronic print 5 soldering points appear on wich the feathers are attached. Carefully heat these points with a soldering bolt and twist the feathers 180 degrees with a tong. The feathers of the lower manual are much more difficult to reach.