Radical shock treatment is failing (6)

I believe the answer is:

defect

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'is failing' is the definition.
(I've seen this before)

'radical shock treatment' is the wordplay.
'radical' becomes 'def' (I can't justify this - if you can you should believe this answer much more).
'shock treatment' becomes 'ECT' (ECT is an example).
'def'+'ect'='DEFECT'

Can you help me to learn more?

(Other definitions for defect that I've seen before include "error" , "Blemish, fault" , "'Flaw, imperfection (6)'" , "Desert and join the other side" , "Shortcoming" .)

I've seen this clue in The Times.

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