To remove the 4 tinnerman washers that are pushed over the 4 plastic posts without damaging anything, just use a sharp pointed pick and gently pry opposing pairs of the teeth up away from the plastic pin where they dig in. You only need to pry just enough to lift the tooth off of the post, any more and you will snap it, its brittle spring steel.
Once you get them off, you can reuse them by squeezing them nearly flat with pliers.
This method works also. Gotta love GM for the cheap fastening methods they used.
Bob