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Hi Dudley, my name is Jason.
The only thing that would be holding that sleeve in place is corrosion. To get it out without destroying it might not be possible. To get it out..... see if you can bend part of it with a hammer and sharp chisel, after that, grab on to it with some needle nose vice grips and twist and pull. You can still get replacement sleeves. In fact most people replace the sleeve when they replace the thermostat. Is there a reason you need to remove it in the first place?