If you see the couplers sagging, then the coupler has vibrated during shipping and the hole that the coupler screws into has enlarged. Tightening the screw will not help since the screw hole is slightly larger now. I had a few of these engines with the couplers detached and sagging. Since Lionel did not put any packing material around the coupler during shipping, the coupler would vibrate up and down and cause the hole that its screwed into to enlarge. It would either sag at this point or the screw would easily back out or fall out. Remember, the coupler is screwed into plastic. The plastic gives a little. All these problems with the couplers could have been avoided with a few pieces of styrofoam on each side of coupler during shipping. My advice, tell your dealer to inspect both couplers before shipping out. If couplers are okay, tell him to add packing material around front/rear coupler. I had my dealer do this and it worked out perfect. No problems.