Tangentially related: Boston Dynamics' BigDog, which utilizes hydraulic actuators, would constantly leak hydraulic fluid while operating, be it through normal weepage or catastrophic leaks (e.g. burst hoses). Initially, they used petroleum-based hydraulic fluid, but as they began to operate out in the woods etc, this proved to be untenable, so they eventually switched to using a vegetable-based hydraulic fluid that would biodegrade within a month.

Bonus: when catastrophic hydraulic leaks inevitably occurred and sprayed hot hydraulic fluid over the hot exhaust, you would be rewarded with the lovely smell of a deep fryer!