Fixed my Canon LIDE 25 with the help of this manual.

There are only 2 screws with our machine. First remove the 2 screws (covered by the stickers in the back - yes the round circles are stickers)

Then turn over, carefully remove the plastic on both sides with a sharp knife (they are glued). Afterwards the glass comes out by pushing in a bit and lifting out.

Now place the middle rod in its grooves with a small pin midway that goes into a small hole. (if the scanner head is in the beginning push it a bit)

Then carefully place the two screws back. Run a test scan to see the head is OK. Then place the glass back by placing at the end first and when inside the end turn the scanner upside down and slide the glass to the end. turn over pull the glass a bit to the front. return the two plastics on the side that were glued (the glue is sticky and still good).

Hope this can help somebody.