My fix was to buy a Torx 5 screw driver, remove the 2 screws in the SDCard corner, snap off the back cover, and take a look. I didn't see the SDCard, so I just tapped SDCard corner on my desktop and it fell out. Seems I missed the slot altogether. Slot and spring action undamaged.
The insertion technique that's worked best for me is to put the SDCard on my fore finger and gently move it into the slot with the Nook horizontal face up, then click it in with my finger nail.
Hope this helps someone.