Favourite part I am hesitating to go after — it requires refinement (9)

I believe the answer is:

petroleum

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'hesitating to go after it requires refinement' is the definition.
I can't judge whether this defines the answer.

'favourite part i am' is the wordplay.
'favourite' becomes 'pet' (synonyms).
'part' becomes 'role' (eg a theatrical role).
'i am' becomes 'um' (I can't justify this - if you can you should believe this answer much more).
'pet'+'role'+'um'='PETROLEUM'

Can you help me to learn more?

(Other definitions for petroleum that I've seen before include "It helps in getting things moving" , "Hydrocarbon fuel" , "Hydrocarbon oil" , "Fuel oil" , "Oil well product" .)

I've seen this clue in The Times.

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