HP 3312a function generator - how to get covers off!

[TonyOldTimer]

I have noticed my previously acquired HP 3312a have a loose BNC connector.  I was able to get the side rail (the one with the carrying handle) off.  However, I was not able to get the top and bottom covers off.  As far as I can tell, the covers are just formed thin aluminium metal painted gray, and held by 4 flat-head screws (two for each cover) to the frame.  I have removed the four screws, and can even see the gray covers through the screw holes.  I even used the holes of the bottom cover (see attached pic) as leverage against the frame, but it would not even budge.  Are the covers held together in some other ways?  Could the covers have been glued to the frame by the previous owner?

Appreciate any pointers.

[bdunham7]

On the backside of the unit there should be a single screw in the middle of each cover.  Often they are covered by calibration seals if there are any.  If you unthread that screw, it should pull the cover back as it goes and then you lift it off.  If the screws come out, just pull the cover backwards manually. 

[TonyOldTimer]

@bdunham7,
  Yes, you are absolutely right.  How on earth am I to miss those two screws hidden under those yellow labels!
Thanks.