Philicorda GM751 Organ Keys Removal

Hello everyone, first of all my apologies writing in English, i come from Greece :)
I found this lovely organ for free at a local flea market and i love it.
It is the latest 751 model, fully transistorized, like the 752 model, no tubes-neon bulbs at all.
It was in a garbage - bad situation, almost defective. After having restored and fully repaired it so far(power cord-fuse replace, full recap,replaced some broken polystyrene capacitors, changed about 10 BF194-5 transistors and pair of AC187-8 Germaniums, contact-switch cleaning) this beauty came to life again, with lovely reverb and nice sound.
Now the only problem left is that i get intermediate sound in 8' voice tab for only two notes. After having tested everything i noticed some broken-cold solder joints in the pcb board under the keys, it is the pcb that is connected with the key contacts, placed in a very hard accessed position.

Any ideas on how i can access this board?
It seems like i cannot unscrew those "red" screws from underneath, they are "factory sealed" with red adhesive.
So my best bet i think is to remove some keys.
I unscrewed the front screw that keeps in place a key but now i cannot manage to get it out from this plastic white mechanism.
It is not a case like this (this is the early tube version in the link):

So i am stuck here ...