It's done!.. If one knows what to do and has proper tools which is a torx screwdriver preferably with a short handle, it's a half an hour job.
The plastic covers from both sides of the seat bottom has to come off or a bit loose to reveal where the ends of the wires are. Actually i could better and faster do the job if i were able to remove the plastic headrest-holding tubes from the seat. Then it would be possible to remove the backrest from the skeleton. Then it would be possible to remove the complete mechanism from the seat. I have done with a small tear on the sponge part of the seat which can not be seen with the cover on.