Crude fluid made better (5)
I believe the answer is:
cured
'made better' is the definition.
(I've seen this before)
'crude fluid' is the wordplay.
'fluid' indicates an anagram.
'crude' is an anagram of 'CURED'.
(Other definitions for cured that I've seen before include "Rehabilitated" , "Of ham, smoked or salted" , "Healed or salted" , "Remedied" , "Successfully treated" .)