I had the same problem. I soaked (kept on applying) liquid wrench to the outside diameter of the steel housing. Mine were screwed through the back. After loosening by twisting and a nudge with a screwdriver, they became free. I mended the cans with steel putty and replaced the lamp sockets which are readily available at auto parts stores. See threads on LED replacements - sounds promising. I've seen the entire aluminum casting assy on ebay, but for me it was too difficult to remove the interior.
New England Unit
Metropolitan NY Unit