Sterling properly shared out, but not in a very bright way (5)

I believe the answer is:

dully

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'shared out but not in a very bright way' is the definition.
I can't tell whether this defines the answer.

'sterling properly' is the wordplay.
I cannot quite understand how this works, but
'sterling' could be 'l' and 'l' is located in the answer.
'properly' could be 'duly' (I've seen this in another clue) and 'duly' is found within the remaining letters.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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