Observant legatee, say, turning head on parking (10)

I believe the answer is:

percipient

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'observant' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for percipient that I've seen before include "Observant" , "Showing acute insight" .)

I've seen this clue in The Guardian.

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