Chanel Ballet Flat Black Patent Leather Toe & Heel

Enjoy these darling CHANEL Ballet Flat with black patent leather toe and heel and lace body. Perfect for summer and fall. Size 36. Fits a US 5.5 easily. But likely too small for a US size 6. Gently used. On the left heel, outside panel, there is a shiny substance. See photos. I don't know what it is and I don't want to ruin the shoe trying to remove it. You can't see the mark when the shoes are on your foot. The rest of the shoe is in maticulous shape. Gently worn sole.