A new door is bolts, hinges, and a spring under real tension - not a project to learn on a ladder. The spring alone can put someone in the hospital if it's wound wrong, and on a door this age the track is probably bent or pitted in ways that aren't obvious until the panel's already off. If you're set on doing some of the work yourself, swapping weatherstripping or a broken roller on an old one-piece door is reasonable. Replacing the whole door, resetting the track plumb, and balancing a new spring to a jamb that's settled over forty years is not a weekend skill, and a door that's out of balance by even a turn or two on the spring will wear out an opener fast. For the full install we come from Jupiter, 11 miles out, so there's no same-day walk-in option - you're scheduling a job, not catching a drive-by.