I am not certain but I think the black thing is a seal of some kind for the RD cable. Jagwire cables come with something similar but I never read the directions to see what it is for.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk