Q: It started an oily substance leak but oil level reads full. It soaked a piece of cardboard and gravel underneath in one night.

Even though the level reads full, it could still be an oil leak. It only takes a very small amount of oil to make a huge mess. Even just a few ounces would make a huge mess, but would be hard to distinguish the loss of it on a dipstick. It could also be transmission fluid, power steering fluid, or even potentially brake fluid. I would check all of your fluid levels, and make sure that they are full.

Next time leave a white napkin on top of the cardboard, to help determine what color the leaking fluid is. Red to dark red fluid is usually automatic transmission fluid, golden brown to dark brown is usually engine oil or potentially power steering fluid, and light amber fluid is usually brake fluid, though could also be power steering fluid.

Since it seems as though the leak could be severe, it should be diagnosed by a qualified technician, such as one from YourMechanic. They can then also evaluate the severity of the leak and provide a repair suggestion and if you can wait or not.