Old model due for discharge (5)
I believe the answer is:
exude
'for discharge' is the definition.
(I've seen this before)
'old model due' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'model' indicates anagramming the letters (the solver must model the letters into a new form).
'due' anagrammed gives 'ude'.
'ex'+'ude'='EXUDE'
(Other definitions for exude that I've seen before include "Seep" , "Be slowly discharged" , "Give off, odour or sweat" , "Long-legged wader" , "Exhibit (via the pores?)" .)