Work in car construction revealing source of oil (5)
I believe the answer is:
copra
'source of oil' is the definition.
(I've seen this before)
'work in car construction' is the wordplay.
'work' becomes 'op' (common abbreviation for 'opus').
'in' indicates putting letters inside.
'construction' indicates anagramming the letters (answer constructed from certain letters).
'car' anagrammed gives 'cra'.
'op' placed inside 'cra' is 'COPRA'.
'revealing' is the link.
(Other definitions for copra that I've seen before include "Coconut's kernel" , "Dried coconut meat" , "Dried coconut kernel" , "Coconuts provide" , "Oil producer" .)