"You're the One That I Want" musical (6)
I believe the answer is:
grease
'you're the one that i want musical' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for grease that I've seen before include "Musical that sounds like a country" , "Lubricating agent" , "Possible cause of slip-up" , "'Thick, fatty oil (6)'" , "Mechanic (informal)" .)