Key worker making some faulty pistons (6)
I believe the answer is:
typist
'key worker' is the definition.
(I've seen this before)
'some faulty pistons' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'TYPIST' can be found hidden inside 'faulty pistons'.
'making' acts as a link.
(Other definitions for typist that I've seen before include "Keyboard user" , "Key worker" , "The old-style secretary, for one" , "Keyboard operator" , "Person at keyboard" .)