MB3 163a: Putting Oil on Shoes on Shabbos (327:3-4); Medicine on Shabbos (328:1-2)

Oiling shoes on Shabbos - new vs. old (עיבוד). Putting oil on your foot before putting your shoes on.

Taking medicine on Shabbos for a slight discomfort is prohibited. An איסור דרבנן can be violated for a "חולה שאין בו סכנה" (non-life-threatening but needs to lie down).

It is a mitzvah to desecrate Shabbos for a life-threatening illness.