after 5 full clears ( means 'all' side areas ) a single one 'could' ( should ) drop, whats not happen sometimes....
imo, there could be a cube material drop for each time rng based like arcane shards, that for a recipe to cube an oil of the following list
for example, clearing one temple in act 3 leads to atleast 1 shard wich can be cubed to 1 oil, when stacked to 5 of them
lets say an oil alchemy extract shard
Oil of Greater Luck: found within the Cave, the Hole and the Pit on Hell difficulty.
Oil of Augmentation: found within the Stony Tomb, the Halls of the Dead and the Ancient Tunnels on Hell difficulty.
Oil of Intensity: found within the Arachnid Lair, the Swampy Pit, the Flayer Dungeon and the temples which stand in Kurast on Hell difficulty.
Oil of Conjuration: found within the portals and the optional caverns in Act 5 on Hell difficulty.
how you thinking about that ?