Corny actor in Greater Manchester (6)

I believe the answer is:

oldham

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'greater manchester' is the definition.
The definition suggests a singular noun which matches the answer.

'corny actor' is the wordplay.
'corny' becomes 'old' (I can't explain this - if you can you should give a lot more credence to this answer).
'actor' becomes 'ham' (ham actor is a kind of actor).
'old'+'ham'='OLDHAM'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for oldham that I've seen before include "Pennine town in Greater Manchester" , "Town NE of Manchester, Churchill once its MP" , "Northern town" , "Town near Manchester" , "Town north-east of Manchester" .)

I've seen this clue in the Evening Standard.

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