More of old retro music, say (5)
I believe the answer is:
extra
'more' is the definition.
(I've seen this in other clues)
'old retro music say' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'retro' shows that the letters should be reversed in order (retro is Latin for 'backwards').
'music say' becomes 'art' (music is a kind of art).
'art' reversed gives 'tra'.
'ex'+'tra'='EXTRA'
'of' acts as a link.
(Other definitions for extra that I've seen before include "Player with no lines" , "Player taking little part" , "One playing small part" , "Bit actor in film" , "particularly" .)