Hedonistic excuse certain to spot ruler (8-7)

I believe the answer is:

pleasure-seeking

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'hedonistic' is the definition.
(thesaurus)

'excuse certain to spot ruler' is the wordplay.
'excuse' becomes 'plea' (I've seen this in another clue).
'certain' becomes 'sure' (synonyms).
'to spot ruler' becomes 'seeking' (I can't justify this - if you can you should believe this answer much more).
'plea'+'sure'+'seeking'='PLEASURE-SEEKING'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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