Over time plug bargain (5)
I believe the answer is:
steal
'bargain' is the definition.
(I know that bargain can be written as steal)
'over time plug' is the wordplay.
'over' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'plug' becomes 'seal' (seal can mean a plug or bung).
't' inserted within 'seal' is 'STEAL'.
(Other definitions for steal that I've seen before include "Creep" , "Thieve" , "Pilfer" , "Make off with" , "Whip" .)