Undercoating oil is a jelled vegetable oil based product - often coloured for identification - and VERY effective. Often also contains lanolin - which helps set it up, like a wax.
Works AT LEAST as well as hydraulic oil - and is not considered a polutant as it is totally biodegradeable. Seaps into joints to provide hidden rust from starting. On cars and trucks don't spray it on engine or powertrain components. Then it's not hard to tell it is NOT an oil leak