Excessively flattering; oily (8)
I believe the answer is:
unctuous
I believe this clue is a double definition.
'excessively flattering' is the first definition.
(I've seen this before)
'oily' is the second definition.
(I know that oily can be written as unctuous)
(Other definitions for unctuous that I've seen before include "Smarmy" , "Excessively flattering" , "Falsely ingratiating" , "Excessively ingratiating" , "Sycophantic - oily" .)