Remove GEM S3 keys

I have a 30-year old Generalmusic/GEM S3 in good working order, but the keys have yellowed considerably. I plan on using Syntaur’s recommended technique for bleaching the keys, but my problem is how to safely remove the keys? The GEM S3 has a Fatar keybed, but there is an extra linkage for polyphonic aftertouch, and I have no idea how to disengage it without damaging it. Anyone with experience on how to do this safely?