Earlier this week I tried to retrobrite my spacebar with no luck (the sun disappeared) and when I tried to open it I noticed it was a lot harder! Now it's impossible.

I'm not the kind of person who uses silicon lube everyday...(if you see what I mean) I did a google search and it is very hard to find some for anything else than latex and other things... 

I did finally find some, rather cheap actually, on amazon for 6€, it's a Facom silicon lubricant. Facom is a French brand, you probably haven't heard of it.

It says it's for rubber and plastics.

What matter of terrible thing have gone wrong with it?! I thought it was just some plastic but apparently it was lubrificated and what I did is get rid of what made it work. Silly me.

You're sure it won't damage the plastics?

BTW: I didn't really follow this guide. I knew it wasn't the right procedure for the screen. I used the Apple service video for the Mac Portable on Youtube instead