Old, sadly due for discharge (5)
I believe the answer is:
exude
'for discharge' is the definition.
(I've seen this before)
'old sadly due' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'sadly' indicates an anagram.
'due' with letters rearranged gives 'ude'.
'ex'+'ude'='EXUDE'
(Other definitions for exude that I've seen before include "Discharge by sweating" , "Discharge (something) slowly" , "Discharge (eg, moisture)" , "Secrete" , "Ooze out or show freely" .)