Pressed into service though old (4)
I believe the answer is:
used
I believe this clue is a double definition.
'pressed into service' is the first definition.
(I've seen this in another clue)
'old' is the second definition.
(as in used or second-hand items)
'though' acts as a link.
(Other definitions for used that I've seen before include "Utilised" , "Accustomed - exploited" , "Not fresh" , "Availed oneself of" , "Dues (anag.)" .)