Quoted from ArgosySK:I had a similar problem on my poker face. Occasionally the power would go out when scoring 5000 points. I could play 10, 20 games and no issue, then three games in a row it would turn off.
It turned out one of the Lock relay switches wasn't close enough so every once in a while it would just let go. A little tweak and it hasn't failed since.
Have him check if it happen at 500 or 5000 or both. and does it happen on the left side too?
This may help narrow down which circuit maybe causing the issue.I would also trace the path of the right kickout hole to see if a solder bead or a cross connection with another circuit has happen.
Also check trace the motor. sometimes the circuit is not complete to keep the motor running for the 500/5000 points.
Don't think there's much chance of talking the owner through this one as it is not an easy fix for someone who knows nothing about pinball repair. Looks like a road trip for you goldenboy232. Maybe you can make it a fun trip and find a pinball machine to buy along the way. 
