The ball return kicker problem is fairly common on Gottlieb games. It's usually caused by that oblong hole. It allows the ball to move too much to the right as it launches to the trough. This makes the kicker hit at the wrong angle.
I take a small screw and screw it sideways into the edge of that hole on the right side. It doesn't need to stick out much. Just enough to keep the ball from rolling all the way to the right as it kicks. I top off the screw head with some liquid electrical tape to keep it from scratching the ball. A nylon screw would be even better.