You should always use sewing machine oil only. You could stain fabric if you use another type of oil, and some other oils can gum up over time. When you oil, make sure you take the end cover off the machine and oil the parts behind the cover. See the two oily wicks at the end of the two shafts in the picture? That's how they should always look. If they get dry, it can cause problems.
Changing the lower feed dog and /or the throat plate the feed dog comes up through should be done if the parts are worn out or broken, but that doesn't happen very often unless the machine was used in a factory.
No one lives forever, the trick is creating something that will.