Regarding the story of Chanukah and the need for tahor oil, I recall hearing in a shiur one time that there are 4 things which are not susceptible to tumah from the Torah; oil (a subset of mashkin) being one of them (though it is a machlokes tanaaim, we come out l'halacha according to the opinion that it is not m'kabel tumah). Furthermore the maggid shiur stated that though oil can become tamei mi'derabbanan, that enactment was not extended to the oil in the temple (mashkei beis mad'bachayim). Thus the oil in the Temple, even those jugs whose seal was broken, weren't even tamei mi'derabbanan. If so why was there a need to produce new oil?
The Sefer Shalal Rav brings many answers such as that rule only applying while the Mizbeach was functional.
Another very clever answer he brings (which seems to me to be the best one) is that Rav holds (See top of Pesachim 17a-רב משקי בית מטבחיא תני, אבל משקי בי מדבחיא מטמא with Rashi D"H Midi Hu- משקה המטבחים דם ומים אבל משקה מדבחיא היין והשמן שהם משקה המזבח גזרו רבנן טומאה עלייהו) that the oil can become Tamei, only the blood and water can't become Tamei.
Shmuel, who argues (See Pesachim 16a- הניחא לשמואל דאמר דכן - מלטמא טומאת אחרים, אבל טומאת עצמן יש להן – שפיר) holds that the word דכן does not mean that they can't become Tamei, it means that they can't be Metameh other things, but they themselves can become Tamei.
Therefore according to both Rav and Shmuel the oil could become Tamei!