The aluminum hinges after decades are going to have worn sockets allowing some door shift. Typically with door hinges it is the top hinge that takes the most wear. You might test for this by swapping top and bottom hinge, or just order two pair from Scamp
store. If you can call and order and ask to have shipped US Postal you might save a chunk of money. UPS and FedEx have steep rates in that part of the country, web site store the shipping is murder.
The hinges themselves have a little play at the mounting bolts. Not a lot but with a second person helping one can loosen the bolts, shift the door, hold it in place and re-tighten the bolts to adjust the angle a bit.
You might also check for where the fiberglass is attached to the floor between door and front corner. The fiberglass sides are attached to the wood floor with fiberglass cloth and resin used like a tape. Moisture can cause wood surface to deteriorate and allow fiberglass to pull free of the floor allowing wall to shift a bit.
Floor does not have to be rotted or anything just softened enough on the inside that the surface wood allows the soaked in fiberglass resin to pull loose. At that corner of the trailer you have the door (never noted for a great seal) the door window and possibly a front window, all points that will allow water in.
Take a look at the square tube that braces the wall along the hinge side of the door opening, make sure it is riveted tight to the wall and has not pulled loose.
I'm pretty sure after over 30 years some wall sag is inevitable, think about it, gravity has been pulling the roof down so the walls can tend to bow outward, it's like our little marshmallow has been squished just a bit. Even a stationary house gets some shifting in the door frames after 30 years.