I didn't know about this nerf until now because I hardly buy this upgrade.
The duration is 2 seconds shorter on Steam.
↑ Flash
↑ Steam
So,
tier 1: Oil lasts 2 seconds on Steam, and 4 seconds on flash and mobile.
tier 2: Oil lasts 4 seconds on Steam, and 6 seconds on flash and mobile.
tier 3: Oil lasts 6 seconds on Steam, and 8 seconds on flash and mobile.
didn't everyone complain it is too expensive for what it does? Now it became worse. 650 gold is better spent elsewhere, e.g. Falconer 600, Barrage 550, ToW 650, Sneak Attack 525.