The lever that you flip engages with a pair of keepers that are attached to the jamb on the latch side. If it no longer locks, here is the most likely thing that could be happening. First, roll the door closed... or rather, ALMOST closed. If you leave it 1/8 open at the bottom, it should also be 1/8 open in the middle and at the top- when looking at the amount of light that comes past the door. If this is not straight, it usually means the rollers need to be adjusted. The rollers are accessed from the ends of the door, in the space directly above the track. You need a VERY long phillips screwdriver to adjust these.... 10 or so in length. Turning the latch side screw clockwise will raise that side of the door and increase that 1/8 gap on top, while turning the screw on the opposite side clockwise will raise that side of the door and close any gap on top. By making that adjustment you will make sure the door is contacting the latch side jamb EVENLY, not crooked. I have never had any other problems with this type of door, so if that doesn't help, you might need to be more descriptive with what's wrong, or include some pictures.

Yes - longer height on one side - not width... welding sounds like a hassle.

Hinges