Where is Janey when you need her? (Janey has the voodoo with Google to find the perfect post.)
My 401 was nasty and I could not move the knobs last year. I also found some posts by J. Miller that were helpful, but could not find them today. What I did was search for the 401a and kept on looking and following links that were in the posts. As I understand it, many of the good sewing machine mechanics moved over to VictorianSweatshop.com. J. Miller and ArchaicArcane are two that don't post here anymore. Read their posts if you can find them. These are the suggestions I received.
401a problem
Found this one
https://www.youtube.com/watch?v=mdaWx1gGZWg