This was posted in a different forum 10 years ago:
"The plastic case is pressed onto the steel base, there are internal one way grippers that hold the case on. I have removed these by taking a two inch wide putty knife and wrapping the end of the blade with several layers of masking tape. Then insert the blade between the bottom edge of the plastic case and the steel base and twisting the blade slightly to put upward pressure on the case. Go around all 4 sides of the transformer and repeat the process, you should start to see the plastic case moving up from the steel base. Continue until the case comes off. Good luck. Fred Hachmeyer firstname.lastname@example.org"