Valet uses oil for a change, being unpredictable (8)

I believe the answer is:

volatile

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

I don't understand the remainder of the clue.

(Other definitions for volatile that I've seen before include "Fickle; tending to vaporise" , "Liable to unpredictable change" , "Easily evaporated" , "A live lot being changeable" , "Subject to sudden change, temperamental" .)

I've seen this clue in The Irish Times.

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