Any/all Above is possible...
or something spilled or Brake Fluid got into Spare tire well and drain thru a drain hole at bottom.
RF Brake has a tube above the steering rack. If that leaks, brake can damage the aluminum rack body. (B-fluid Leaks at the wheels can do same for alloy rims.)
Brake fluid isn't just feels like oily, can/will "burn" your skin too and doesn't smell like most oils.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave