I've done the "eyes on the track" thing many times actually, using a flashlight too. I don't have good vision to begin with but I do see the front roller moves fine and from behind the engine the rear roller looks OK yet something at just beyond the mid-point of the engine is hitting solidly because as I push it forward, it reaches a point where it just hits a wall. If I force it, it derails.
Oddly, it rolls smoothly and flawlessly on another 1122 near it, either front to back or back to front. The only difference between the two is one has the auxiliary rail (the one it works on() and the other does not. I'm thinking about ordering the rail from Brasseur.
