Darkslide stuck in Mamiya RZ filback. How do I get it out?

I just bought a supposedly working 6x6 filmback for my RZ off ebay. When it arrived, I mounted it to the camera and was unable to remove the darkslide. Taking it back off the camera, manually removing the darkslide by depressing the little interlock pin in the mount doesn't allow the darkslide to be removed either. In fact, I can't even detect any play in the darkslide (other backs let the darkslide jiggle around a few tenths of a mm even with the interlock retaining the darkslide in place).



It seems as though the darkslide must be physically jammed in its groove. Anyone have any ideas on how to get it out?