My 401 was easy to work on since the previous owner took excellent care/maintenance. I just went to the Videos on the 401 along with my manual that luckily came with it. Sometimes in depth multiple manuals can be overwhelming and thence nothing is done. The cleaning and maintenance is procrastinated. My machine is working great. I followed the instructions that came with my machine and the videos. I studied them and kept them nearby as I worked on it. I didn't really do anything to the cam stack like disassemble. One part of the linked manual makes it hard due to some of the diagram photos just aren't visible. And it talks about dipping the machine into varsol. Doesn't take a whole lot to loosen up lube. A little lube on lube will help loosen it up. Just be patient. Clean off as much as you can with a stiff (but not wire)brush. I'm not an expert on vintage machines by far, I'm just saying what works for me. Of course I got lucky since the previous owner took great care with her machine. She had to, she was an interior designer who made drapes/curtains and upholstered a lot and made different bed coverings. I could go on and on. But check out the different YouTube videos. Just search the 401. Good luck.