There's a plastic rivet/plug thingy (appx 1" long and 3/8" - 1/2" diameter)that has a series of semi flexible ridges that look like screw threads. The ridged portion passes through a hole in the other part of the cover, thus keeping them joined together. It's impossible to pull off since the ridges have a much larger diameter than the hole. The head of the rivet/plug is actually glued on to the yellow/white hard foam that is packed into the black plastic cover, so the best way to remove it is to break the glue seal and the 2 pieces come apart. I glued it back in place on reassembly with no problem(although it sounds like you won't be reinstalling). The head of the rivet/plug is shaped exactly to the contours of top part of the plastic cover, so it it is easy to glue back in exactly the same place. I was going to take some photos when took mine off but couldn't find my camera at the time
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