Welcome to the forum.
In addition to the link TedEbear posted, I found that the main problem is the push plate rail(s) is out of alignment. Depending on your point of view, when the motor turns counterclockwise, more pressure is put on the left rail. When it is running clockwise, more pressure is placed on the right rail. You can see this if you watch closely as the motor advances the "pusher". If you don't notice this, look for wear, as instructed in the post, and align the rail.