Do you see any wetness underneath? If not, the most likely suspect is a seal in the rack and pinion steering gear assembly. Loosen one of the smaller clamps on one of the bellows boots, then pull down a little on the boot with a pick. If fluid runs out the assembly must be replaced.

If there is wetness all over, you can wash the area with engine degreaser, then add a small bottle of dark purple dye to the fluid. Later, you search with a black light. The dye will show up as a bright yellow stain that you can follow back to the source.