Perfectionist left in label (8)
I believe the answer is:
stickler
'perfectionist' is the definition.
(as in a stickler for the rules)
'left in label' is the wordplay.
I cannot really see how this works, but
'left' could be 'l' (common abbreviation) and 'l' is present in the answer.
'label' could be 'sticker' (synonyms) and 'sticker' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for stickler that I've seen before include "Someone who insists on something" , "One insistent on things being just so" , "One who is fussy" , "Pernickety person" , "One insisting on correctness" .)