The giveaway on a house this age usually isn't a door that's stuck shut - it's a door that's running crooked, or has already come off one side of the track and is hanging at an angle in the opening. On the lighter steel panels common to late-1960s builds, you'll often see it start small: a scrape noise low on one side, the door catching for a second on the way down, then one bottom corner sitting noticeably forward of the other.
Sometimes it's sudden - a cable pops, or a roller finally shears after years of wear, and the door drops half off the rail all at once. Either way, the panel on these older narrow-track doors is light enough that it can look like it's still holding its shape even when the hardware underneath has already given out. If your door is sitting crooked in the opening, off by even a small amount, treat it as off-track and stop running the opener until someone's looked at the track itself.