No single thing worked for me.
Used a combination of cleaners (Dawn, Simple Green, Kaboom, Goo-Gone, Magic Erasor, etc.) with a combination of applicators (rags, rags at the end of a flat blade screwdriver, mop, toothbrushes, buffer pads, manual wire brushes and wire wheels on a drill, etc.). Added both steam cleaning (where I could insert the tool heads) and power washing. Everything helped.
Did a section at a time until it was all finally done. Wasn't really horrible in the first place, but I wanted it clean enough everywhere so any new dirt/oil/water source is immediately obvious.
Sounds like in your case you'll need to start first with absorbent material (e.g., Zorb pads) to capture oil... and then you'll want to identify the oil source and fix that.
-Chris