After 1972 (before my time), Trillium used the L-300 only.
Bargman developed the L400 when they ran into trouble with the very old L-300 tooling. They suggested ending the L-300 back then already. Since they were occasionally out of the L-300 locks, we changed all the molds to accept the L-400
These are the only 2 locks the factory used on the 1300 & 4500 models.
Lubricate the inside parts. That will extend its life.
Door: Yes, the center seam didn't always line up properly on the door. We had a variety of molds, and couldn't take the time to match them all up.
Keep in mind, that in the 70s, there wasn't the drive for 'perfection', as we have today. Even though we were ahead of every one else in quality, we overlooked this in our strive for market share.
Hinges can not create door sag, unless the screws are so loose to the point of falling out. Over the years many have tried to adjust the door by moving the hinges, but this didn't work out well. Each trailer would have a unique solution.
Catch not holding: The best way to analyze, is to stand inside the trailer. and look closely at how the catch and door lock overlap. Usually, the tongue doesn't mate well with the catch. This can be adjusted by carefully bending the catch so that it will stick out further. It's not the easiest thing to do. It requires patience and trial & error with vise grips. The factory workers adjusted every trailer like this.
Hope this helps.