Fixing a WPC Ball Trough

My Judge Dredd had plenty of problems: one in particular was the ball trough. It looked like it had been previously repaired with pliers, and was incapable of reliable feeds. A previous owner had labeled the game to be used with 3 balls only.

Just about every WPC game with the new trough has this problem. You can shim the trough or replace it entirely. Or you can endeavor to fix it. 

Here's the outside of the trough, showing the wrinkle from a previous repair. And the inside, showing the ball dimples. These dimples are made by balls sitting in the trough. When a ball drains, it hits the top ball in the pile. Every ball takes a little shock, some of which it passes on and some of which it transfers to the softer trough material. Over time, the trough develops perfect ball dimples that  will hold balls back in the trough. This holdback usually manifests itself as multiballs missing balls.
Here's the outside from another angle. Normally, the dimples can be filed out with a small file at about 45 degrees to the edge of the trough. They don't have to be eliminated, just blended in to allow the balls to roll smoothly. In this case, we have the wrinkle to contend with.
The Harbor Freight arbor press is a very handy tool. Here I am abusing it by placing the bent-up trough bottom between the anvil and the post, and hammering on the post. This process flattened out the nasty wrinkles from the pliers repair. The dimples still needed to be filed out, but the hammering also reduce the dimples. Here's how we test the trough. The top of the trough should be level. The file is there to raise the bottom to achieve that. Then we can roll balls to see if the dimples and wrinkles are fixed. If the ball rolls smoothly, and cannot be placed in any position other than the end, then we are OK.
Here's the trough after hammering and filing, followed by emery papery then some wet or dry. The wrinkles are gone. Side view. Much better!
Here's the inside of the trough. Ugly, but functional. the balls roll freely and do not hang up. Installed in the machine. Note the auto ball stop, which prevents balls from falling out when the playfield is raised.