Oozing spot on errand boy (7)
I believe the answer is:
seepage
'oozing' is the definition.
('seepage' can be a synonym of 'oozing')
'spot on errand boy' is the wordplay.
'spot' becomes 'see' (I've seen this before).
'on' says to put letters next to each other.
'errand boy' becomes 'page' (page is a kind of errand boy).
'see'+'page'='SEEPAGE'
(Other definitions for seepage that I've seen before include "Slow leaking flow" , "Discharge" , "Leaking liquid" , "slow escape" , "Loss from slow leak" .)