Goodbye said to old rogue on Tube returning (6-3)
I believe the answer is:
toodle-pip
'goodbye said' is the definition.
I know nothing about this answer so I can't judge whether this works.
'to old rogue on tube returning' is the wordplay.
'rogue' indicates anagramming the letters.
'on' means one lot of letters goes inside another (as in clothing \'on\' a person).
'tube' becomes 'pipe' (pipe is a kind of tube).
'returning' is a reversal indicator.
'pipe' back-to-front is 'epip'.
'old' with letters rearranged gives 'odl'.
'to' inserted inside 'odl' is 'toodl'.
'toodl'+'epip'='TOODLE-PIP'
Can you help me to learn more?
(Other definitions for toodle-pip that I've seen before include "so long" , "Farewell (informal)" , "Take care" , "Goodbye (dated)" , "Farewell remark - dipole top (anag)" .)