Extra repeats becoming so long (3-3)
I believe the answer is:
bye-bye
'so long' is the definition.
(I know that so long can be written as bye-bye)
'extra repeats' is the wordplay.
'extra' becomes 'bye' (bye is a type of extra in cricket).
'repeats' shows that letters should be duplicated.
'bye' doubled is 'BYE-BYE'.
'becoming' acts as a link.
(Other definitions for bye-bye that I've seen before include "Childish farewell" , "See you" , "Informal repetitive farewell" , "Au revoir for juniors?" , "Ta-ta" .)