WIY, Tuma Hutra Betzibur has nothing to do with oil, it’s about the Tzibur.
Yekke, that’s Lav Davka. The Torah says you need Shemen Zayis, which is a type of oil. It’s a nice Chap to say that it has to come from an actual Zayis, but it’s not really etched in stone. Anyhow, the problem exists only if the iol spring up from nowhere. If the oil expanded itself, the Shemen Ness issue doesn’t come in to play.