More slick, having previously spoken in the Bronx? (6)
I believe the answer is:
oilier
'more slick' is the definition.
(slick can mean oily)
I don't understand how the rest of the clue works.
(Other definitions for oilier that I've seen before include "rather greasy" , "More lubricated or flattering" , "More oleaginous" , "having applied more sun cream?" , "More viscous or slippy" .)