Sally Bowles missing start of stage musical – it's hard work (5,6)
I believe the answer is:
elbow grease
'hard work' is the definition.
(synonyms)
'sally bowles missing start of stage musical it's' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is found within the answer.
'musical' could be 'grease' (Grease is a film musical) and 'grease' is present in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
The remaining letters 'lbw' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for elbow grease that I've seen before include "Hard rubbing (colloq.)" , "Vigorous physical effort" , "Hard physical work (informal)" , "Vigorous physical labour involving hard rubbing" , "Hard physical effort" .)