Badly built car needs a drop of engine oil (9)
I believe the answer is:
lubricate
'oil' is the definition.
('lubricate' can be a synonym of 'oil')
'badly built car needs a drop of engine' is the wordplay.
'badly' indicates anagramming the letters.
'needs' says to put letters next to each other.
'a drop of' indicates taking the first letters.
The first letter of 'engine' is 'e'.
'built'+'car'='builtcar'
'builtcar' is an anagram of 'lubricat'.
'lubricat'+'e'='LUBRICATE'
(Other definitions for lubricate that I've seen before include "Coat with oil to reduce friction" , "Make slippery" , "Apply oil/grease" , "Bribe" , "Oil (a mechanism)" .)