Ive ever seen a machine does not go out of timing on its own.
Have you cleaned the lint out of the bobbin area.
As far as stitches go, you have to regularly oil that machine. If there is dried oil you will have to clean it off. There is a lot of information on this board. You can search here - look in the upper right and type in Singer 401 and see what you come up with. Some will be good repair info some will not be of any use at all.