Part of paint roller that's beginning to work (5)
I believe the answer is:
intro
'part' is the definition.
(I have seen 'Preliminary part ' mean 'intro' so perhaps 'part' could also mean 'intro')
'paint roller that's beginning to work' is the wordplay.
'paint' becomes 'in' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'that's beginning' says to take the initial letters.
'work' indicates anagramming the letters.
The initial letter of 'roller' is 'r'.
'r'+'to'='rto'
'rto' with letters rearranged gives 'tro'.
'in'+'tro'='INTRO'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for intro that I've seen before include "Preamble" , "overture" , "Opening bars of a song" , "Beginning (informal)" , "Prologue, opening (abbr.)" .)