override solenoid is controlled by a payout relay (insert) switch.
there's two payout relays ... one on the hopper and one in the top compartment ... the top panel is called the "insert".
the only thing controlling the payout relay insert coil is a payout relay hopper switch, so you have an odd situation. if the payout relay on the hopper was staying powered, the hopper would continue to run until the safety circuit shut the whole machine down.
if the payout relay on the hopper unpowers like it should at the end of payout, then the payout relay insert should unpower at the same time.
assuming all your pays work correctly, what are the payout relays doing at the end of pay?
I guess the sanest explanation is a problem with the switches on the payout vs. credit key switch. Check the switch with green wire 40-5 and red/green wire 14-2 on the blades. Make sure neither wire/blade is shorting to an adjacent switch.