These are the new all metal (12ga crs) shaft end plates to prevent wire or string from getting off the end of the shaft.
Bonding surfaces of the Bot should be cleaned with IPA soaked swab, then wiped dry with second clean swab. I suggest Gorilla Super Glue.
Put some dabs in the obvious places and gentle lower in place ensuring the alignment of the shaft (rotate when setting).
Hand made by me.