Spring after spring it never fails to surprise me (4,4)
I believe the answer is:
well well
'it never fails to surprise me' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'spring after spring' is the wordplay.
'spring' becomes 'well' (both can mean a source of water).
'after' means one lot of letters go next to another.
'spring' becomes 'well' (both can mean a source of water).
'well'+'well'='WELL WELL'
Can you help me to learn more?
(Other definitions for well well that I've seen before include "Spring twice to express surprise" , "Repeated expression of surprise" , "Surprised expression" , "Fancy that!" .)