Two notes correctly so long (8)

I believe the answer is:

farewell

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'so long' is the definition.
(I've seen this before)

'two notes correctly' is the wordplay.
'two notes' means two substitutions for 'note'.
'note' becomes 'fa' (fourth note in sol-fa notation: doh, ray, me...).
'note' becomes 're'.
'correctly' becomes 'well' (I am not sure about this - if you are sure you should believe this answer much more).
'fa'+'re'+'well'='FAREWELL'

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(Other definitions for farewell that I've seen before include "Parting word" , "Archaic goodbye - good luck" , "All the best" , "Archaic goodbye or leave-taking" , "Goodbye, cheerio" .)

I've seen this clue in The Times.

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