Many an imperfection changes sides (7)
I believe the answer is:
defects
'many an imperfection changes sides' is the definition.
I can't tell whether this defines the answer.
'imperfection changes sides' is the wordplay.
'imperfection' becomes 'defect' (defect is a kind of imperfection).
'changes sides' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'defect'+'s'='DEFECTS'
Can you help me to learn more?
(Other definitions for defects that I've seen before include "Shortcomings; changes sides" , "Abandons cause" , "Faults" , "defaults" , "Flaws" .)