In all honesty, a little lint isn't really harmful but at what point does it become a lot of lint and then cause problems. I bought a Singer401 the other day and it was clean like it had barely been used until I opened up the bobbin area. I did no oiling just lint cleaning. Once the lint was gone the machine turned freely. My guess is they used cheap thread or some linty project but didn't know how to clean it. Sad. oh and I did oil the 401...