Leak part of cross-reference (7)
I believe the answer is:
seepage
'leak part of cross-reference' is the definition.
'seepage' can be an answer for 'leak' (I've seen this in another clue). I'm unsure of the 'part of cross-reference' bit.
'leak part of cross-reference' is the wordplay.
'leak' becomes 'seep' (I've seen this in another clue).
'part of cross-reference' becomes 'age' (I can't justify this - if you can you should believe this answer much more).
'seep'+'age'='SEEPAGE'
Can you help me to learn more?
(Other definitions for seepage that I've seen before include "Slow fluid loss" , "Ooze" , "Slow leaking flow" , "problem with tank" , "Discharge" .)