Gearbox locking up

Hello,

I've recently started having an issues with my aeg (G&G Combat Machine M4 Carbine). Every time I pull the trigger in either semi or auto, the gearbox rotates a little and then stops and completely locks up. The only way to get it unstuck is to take out the motor and manually pull the anti reversal latch.

Things I've tested:

• The motor spins fine outside of the gearbox.
• The battery is fully charged and I've confirmed it's delivering just shy of 9.6v to the motor.
• Replaced the gearbox. The original gearbox started doing it so I ordered a complete gearbox to rule it out. The replacement and original do the same thing.
• Tried a replacement 9.6v battery
• tried a replacement motor of the same rpm.

The gun worked fine before this though it was in storage for an extended amount of time. I'm kind of stuck at this point. Is it worth it to try an 11v battery and/or more capable motor?

I know bringing it to a repair shop would be optimal, but the nearest one to me is a 2.5 hour drive.

Thanks in advance for any advice.