Crossword Genius

Bore audience with Marx, then steal away (4,2,5)

Ross

I believe the answer is:

harp on about

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'bore audience' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'with marx then steal away' is the wordplay.
'with' means one lot of letters go next to another.
'marx' becomes 'harpo' (Harpo Marx).
'then steal' becomes 'nab' (I can't justify this - if you can you should give a lot more credence to this answer).
'away' becomes 'out' (synonyms).
'harpo' put next to 'nab' is 'harponab'.
'harponab'+'out'='HARP ON ABOUT'

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I've seen this clue in The Independent.
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