I am so glad that Wishfulthinking started this thread because I've learned from the posts, copying them to put into my 503 notebook. Regarding Miriam's photo of where to oil under the bobbin, that is another time I turn the machine on it's side to get to anything that moves under it, sometimes even pull out a stray thread with the serger tweezers. Photos and explanations posted on here are priceless.
When Miriam says do not take off the handwheel and stop motion knob, heed what she says. I can show you the cardboard box where a Kenmore 1914 has lived for several years since my resident muscle and favorite helper felt he should remove the handwheel and re-set those parts I have no names for that reside there. That's one I may pay someone to put back together.
Tri-Flow is my friend! I've ordered oil and grease from Sew Classic. It can sometimes be found at bike shops.