In a cupboard at home I dug out a roll of fibre glass mesh, the kind used for gypsum wallboard joints. I cut small pieces of it to use as "rebars" together with the epoxi.
An exemple of the fibre glass rebar. It will now be covered in epoxi, and I did the same on the other side.
While the glue was hardening, I went looking for suitable lubricants. I found a bottle of sewing-machine oil and some spray for nail guns. The sewing-machine oil was fine.
I also made myself a pot of strong coffee...
I continued removing all of the keys, and placing them in their correct order on my desktop
This is what a Tubon key looks like. There is a push-rod with a slotted piece of plastic where the contact spring will fit. In the back end of the key there is a screw and a spring. The tension of the spring is adjusted with the nut. The nut is secured with some sort of loctite.
Using a topsy, I applied some oil to the pushrods.
The pushrod goes through a hole in the keybed, and a felt washer. The keys had a tendency to stick in the holes, so I used a small round file to clean out the holes until the pushrods moved smoothly.
This is what the felt washer looks like.
I went through all keys, because all of them were sticky, with file and oil, and put it all together again. Now the entire keyboard works nice and smooth.
To wrap it up, I connected all of the contact springs, and adjusted them using a set of flat-nosed pliers.
The keyboard is now on a shelf above my desk. I have ordered a four-pin DIN plug so I can connect the Tubon to an amplifier, but until then I will continue the reverse-engineering and take a look at the rat's nest behind the left hand controls. But not tonight.