This fix isn't needed for 1.21+ patch.

Oil indicator feature introduced in 1.12 patch only works in normal game. This simple fix inserts missing Oil effect into abilities_plus\effects.xml making it work in both normal game and NG+.

Use NMM to install or copy the mod folder manually under your "[Path to The Witcher 3]\Mods" folder. To remove the mod use NMM or simply delete its folder from "[Path to The Witcher 3]\Mods" folder.

NOTE: I'm not supporting this, because it's a simple fix with simple install procedure. In case of other xml mods, which modify effects.xml for NG+, use Script Merger to find and resolve conflict.