When I got my car, it came with a large weight bolted to the C4 tranny. I was told by an old Ford technician, who is into vintage Mustangs, that this was done at the factory. He referred to the item as a "Squirrel catcher" and said it was designed to reduce transmission vibration. I cleaned it, repainted it but never used it. Any value in keeping it, or should I just dump it?