Slough crossed by rower, if old wizard on bridge playing role? (4,6)

I believe the answer is:

omar sharif

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'old wizard on bridge playing role?' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'slough crossed by rower if' is the wordplay.
'slough' becomes 'marsh' (both can mean a swampy area).
'crossed by' is an insertion indicator (inserted letters are crossed or covered by others).
'rower' becomes 'oar' (I've seen this in another clue).
'marsh' going inside 'oar' is 'omarshar'.
'omarshar'+'if'='OMAR SHARIF'

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I've seen this clue in The Guardian.

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