Competitor breaking record in mucky film? (4,6)

I believe the answer is:

pool player

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'competitor' is the definition.

'record in mucky film?' is the wordplay.
'record' becomes 'lp' (LP is an example).
'in' indicates putting letters inside.
'mucky' becomes 'poo'.
'film?' becomes 'layer' (I've seen this before**).
'poo'+'layer'='poolayer'
'lp' put within 'poolayer' is 'POOL PLAYER'.

'breaking' acts as a link.
This may not be correct. It may be part of another bit of the clue.

Can you help me to learn more?

I've seen this clue in The Guardian.

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