Trace car from 1966 (4)

I believe the answer is:

dreg

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

I can't explain the remainder of the clue.

(Other definitions for dreg that I've seen before include "Small quantity (of residue?)" , "Trace" , "Small amount left over" .)

I've seen this clue in The Independent.

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