One of my favorite things I've ever read about sewing machines was one where a lady took her machine in for a tune-up because it the feed dogs weren't working. Came back, worked great, but she called the repairman and asked why he took out the felt pad under her feed dogs and didn't replace it. He was pretty puzzled, as there isn't a felt pad under there, until he remembered *which* machine it was. It was the one that looked like it had never been cleaned under the feed dogs, ever in its life. That "felt pad" was the compacted lint of the ages, lol. I just love that story.