I have 401-A--my first machine. 2 years ago, for its 50th birthday, I took it for it's first repair. the belt was slipping and needed replaced.
never had a problem, and sewed my school clothes, kids clothes, and grandkids clothes. Have a viking now, but would never part with my 401A. HUMMM-wonder why the feed dogs still are in great shape, and my viking is on it's 2nd set, and really need to be replaced again. don't make 'em like they used to.