A leak, you understand, to the paper (7)
I believe the answer is:
seepage
'a leak' is the definition.
(I've seen this before)
'understand to the paper' is the wordplay.
'understand' becomes 'see' (synonyms).
'to the paper' becomes 'page' (page is a kind of paper).
'see'+'page'='SEEPAGE'
'you' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for seepage that I've seen before include "running out slowly" , "Loss from slow leak" , "Slowly leaking flow" , "Percolation" , "liquid having soaked through" .)