With vintage machines, people actually looked at what they were doing when assembling them. Recently, my friend's Brother machine stopped working at a very bad time. She was making costumes for the school play which was 3 days away. In passing, she mentioned the fact she had to go sewing machine shopping after work!
20 minutes later (thankfully I keep a good toolbox at work) I had cleaned out the feed dog area, reconnected a spring, and shifted 80% of the grease on to the gears. That's right. Most of what had been applied had not even been placed correctly. Now it runs better than it ever has! Workmanship...