Quoted from arzoo:
I also noticed there's a small unused hole (about screw size) behind the top rail just to the left of the opto mount. It's very close to the back wall, about 3/4" from the rail. Wonder what it was intended to be used for? I might be able to secure and L bracket between the back of the rail and the playfield using that hole, which should theoretically reduce the flex in the rail. Although I could drill a new hole anywhere back there to mount the L bracket.
LTG, What do you think about this? Would this be a possible solution?