Seep or leak out slowly (4)
I believe the answer is:
ooze
I believe this is a double definition.
'seep' is the first definition.
(I know that seep can be written as ooze)
'leak out slowly' is the second definition.
(I've seen this in another clue)
(Other definitions for ooze that I've seen before include "Exude mud" , "Seep out slowly" , "Percolate" , "Mud at bottom of river" , "nap" .)