I remove Synta's factory glue-grease with charcoal-lighter fluid, used for grilling food outdoors. It's a light grade of kerosene, and cuts right through the old grease...
The CGEM is considered too complicated to work on by the average user, which is probably why you're having trouble finding renovation material. Of course, I would work on one regardless, so welcome to the DIY club.
There are folks working on theirs on YouTube...
https://www.youtube.com/results?sear...Celestron+CGEM