Self-Locking Support Peg for 3/4 In. Shelf

Hello! I can't show you the part I need uninstalled because it's still (barely) holding up the shelf. The cabinets were installed before 1992, and I just noticed that the right side of one shelf is suddenly uneven. Uh-oh! The pegs/brackets are rectangular & white, but I think I'll replace them all because the plastic they're made of feels a bit brittle. I hope this info and the pictures are enough for you to guide me. Thank you, Chris Kessler