Right in passion for vital part (5)
I believe the answer is:
heart
'vital part' is the definition.
(I've seen this before)
'right in passion' is the wordplay.
'right' becomes 'r' (common abbreviation).
'in' means one lot of letters goes inside another.
'passion' becomes 'heat' (synonyms).
'r' inserted inside 'heat' is 'HEART'.
'for' is the link.
(Other definitions for heart that I've seen before include "Earth (anag) -- compassion" , "Muscular organ - compassion" , "Body organ" , "Nucleus" , "Feeling" .)