‘The old routine” is right (5)
I believe the answer is:
exact
'is right' is the definition.
('exact' can be similar in meaning to 'right')
''the old routine' is the wordplay.
I cannot quite understand how this works, but
'old' could be 'ex' and 'ex' is present in the answer.
'routine' could be 'act' ('act' can be a synonym of 'routine') and 'act' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for exact that I've seen before include "Demand, extort" , "As a right, demand" , "Precise and strictly correct" , "Precise - demand" , "Precise; extort" .)