Musk perfume finally given after arm stretch (8)
I believe the answer is:
elongate
'stretch' is the definition.
(to elongate is to stretch out)
'musk perfume finally given after arm' is the wordplay.
'musk' becomes 'Elon' (Elon Musk).
'finally' indicates one should take the final letters.
'given after' is a charade indicator (letters next to each other).
'arm' becomes 'gat' (gat is a kind of arm).
The final letter of 'perfume' is 'e'.
'e' after 'gat' is 'gate'.
'elon'+'gate'='ELONGATE'
(Other definitions for elongate that I've seen before include "Stretch, lengthen" , "stretcher will do!" , "Gone late oddly to extend" , "Make longer" , "Stretch lengthways" .)