Sweat as the first lubricant (4)
I believe the answer is:
toil
'sweat' is the definition.
(I've seen this in another clue)
'the first lubricant' is the wordplay.
'the first' becomes 't' (1st letter of 'the').
'lubricant' becomes 'oil' (I've seen this before).
't'+'oil'='TOIL'
'as' is the link.
(Other definitions for toil that I've seen before include "Manual labour" , "Work really hard" , "Drudgery" , "Work extremely hard" , "Hard physical work" .)