Superficial sort breaking leak (4-4)
I believe the answer is:
skin-deep
'superficial' is the definition.
(I've seen this before)
'sort breaking leak' is the wordplay.
'sort' becomes 'kind' (synonyms).
'breaking' indicates putting letters inside.
'leak' becomes 'seep' (I've seen this in another clue).
'kind' going within 'seep' is 'SKIN-DEEP'.
(Other definitions for skin-deep that I've seen before include "Superficial (like beauty?)" , "Stringed instrument" , "The depth of beauty" , "Superficial as beauty is said to be" , "Superficial like body graze" .)