Complained malingering finally has been found out (8)

I believe the answer is:

grumbled

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'complained' is the definition.
(grumbling is a kind of complaining)

'malingering finally has been found out' is the wordplay.
'finally' says to take the final letters.
'has been' becomes 'mb' (I can't justify this - if you can you should give a lot more credence to this answer).
'found' becomes 'ruled' (as in ruling or finding in court).
'out' means one lot of letters goes inside another.
The last letter of 'malingering' is 'g'.
'mb' going within 'ruled' is 'rumbled'.
'g'+'rumbled'='GRUMBLED'

Can you help me to learn more?

(Other definitions for grumbled that I've seen before include "Expressed discontent" , "Complained in a bad-tempered way" .)

I've seen this clue in The Times.

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