Musical right for ship's engineer (7)
I believe the answer is:
greaser
'ship's engineer' is the definition.
(I've seen this before)
'musical right' is the wordplay.
'musical' becomes 'grease' (Grease is a film musical).
'right' becomes 'r' (common abbreviation).
'grease'+'r'='GREASER'
'for' acts as a link.
(Other definitions for greaser that I've seen before include "(Unskilled) mechanic" , "Biker" , "Young motorcyclist" , "An unctuous individual" , "Mechanic - sycophant" .)