Car paint essentially must be in new emulsion (9)
I believe the answer is:
limousine
'car' is the definition.
(limousine is a kind of car)
'paint essentially must be in new emulsion' is the wordplay.
'essentially' says to take the centre.
'must be in' means one lot of letters goes inside another.
'new' indicates anagramming the letters.
The centre of 'paint' is 'i'.
'emulsion' with letters rearranged gives 'limousne'.
'i' put inside 'limousne' is 'LIMOUSINE'.
(Other definitions for limousine that I've seen before include "big car" , "Luxurious car (with a chauffeur?)" , "Large luxurious car" , "Form of transport" , "Luxury car" .)