I've removed the screw cap, the handle mounting screw and a brass color retainer but that's as far as I can go, I think. What I see is a gray plastic cartridge body with the gray square actuating shaft running into it. There are two lots in the metal body where the gray plastic cartridge body edges are visible. Gentle prying at these locations hasn't gotten the cartridge out for me.
Do I need a special tool to extract the offending parts? And, once I get the cartridge out how do I identify the manufacturer so I can find a replacement?