|Most machine (at least the non-computer ones) should be "oiled" ever 8 to 10 hours of use. I am talking about lubricating in the little spots the manual shows. I use Tri-flow since Ray Sewing Machine repair class. It doesn't gum up and collect ick. Plus it has a long an very tiny tube that allows you to put 1/2 to 1 drop of oil in the machine.
annual oiling: I learned to take of the top, side and bottom and, turning the hand wheel slightyl toward me, watch the little parts move. If metal touches metal and moves it gets a drop of oil. This is the major oiling that the repair guys do when you take it in.
I found this at the local bike shop and an auto supply store. My friend had a sewing machine that was "locked" up tight and she liberally squirted this on all moving parts and then repeated the next day. It now moves!