I agree with all of the above. Do be careful with cleaning, especially the 66 as the best cleaning of Japanned machines is with sewing machine oil. The 401 is painted so still need to be careful, but a damp rag and dried will probably work.
For the 401 the best thread I have found to working on them can be found at
Vintage Giggles aka What are they smoking???? particularly post #15. And for servicing the cam stack and stitch selectors this page is good -
https://archaicarcane.com/stuck-in-t...lant-o-matics/ (Not affiliated with link)
A couple of other threads about the 401
Shall I try and get this machine? Shall I try and get this machine?
Janey - Neat people never make the exciting discoveries I do.