Old stock about to come in for free (9)
I believe the answer is:
extricate
'free' is the definition.
(I know this)
'old stock about to come in for' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'stock' becomes 'trite' (I've seen this before).
'about' indicates putting letters inside.
'to come in for' becomes 'ca' (I am not sure about this - if you are sure you should believe this answer much more).
'trite' placed around 'ca' is 'tricate'.
'ex'+'tricate'='EXTRICATE'
Can you help me to learn more?
(Other definitions for extricate that I've seen before include "Free from entanglement" , "Disentangle, release from difficulty" , "get out from difficult situation" , "Free (something) from difficulty" , "wriggle free" .)