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' is an anagram indicator (answer constructed from certain letters).
'car' with letters rearranged gives 'cra'.
'op' placed inside 'cra' is 'COPRA'.
'revealing' acts as a link.
(Other definitions for copra that I've seen before include "Coconut's kernel" , "Dried coconut meat" , "Dried coconut kernel" , "Coconuts provide" , "Oil producer" .)