Judas, apparently, replaced a tractor part (7)

I believe the answer is:

traitor

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

I don't understand the remainder of the clue.

(Other definitions for traitor that I've seen before include "Unreliable figure" , "Betrayer of a country" , "Double-crosser" , "Betrayer of a cause" , "One committing treason" .)

I've seen this clue in the Evening Standard.

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