I recently welded (soldered) the first track of my main. The rail is flex track. I was soon operating 30-50 car trains without diffuculty. I stopped a 30 car grain extra after 30 perfect laps. Then a week later I started the train up. Over the mainstreet overpass on a horseshoe curve, the whole train fell outward with even cars off the table! I soon realized that the track had shifted off the roadbed and was on a graded angle. I rerailed the train and hoped that this was a fluke but it happened again. Is the story that n-scale rail shifts true? I'm now left with the options on regrading my main through 4 feet, using more nail to "retack" the main or just tearing it up and adding new jointed rails like snap track or flextrack, that isn't soldered. Answers and ideas please............