Worked, having been lubricated to a T (6)
I believe the answer is:
toiled
'worked' is the definition.
(toiling is a kind of working)
'lubricated to a t' is the wordplay.
'lubricated' becomes 'oiled' ('oil' can be a synonym of 'lubricate').
'to a' says to put letters next to each other (I've seen this in other clues).
'oiled' after 't' is 'TOILED'.
'having been' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for toiled that I've seen before include "Worked incessantly" , "Worked long and hard" , "Laboued long and hard" , "Worked laboriously and long" , "Struggled long and hard" .)