Loss of oil?

Doing a recent visual, I noticed that the area under the air filter and up around steering pump is coated / saturated with oil. I ruled out the SP leaking. I also noticed that my engine oil was low enough to not register on the dip stick. What is in that area that could be leaking. I've looked and don't see any heavy oil stains or drips where I been parking. I just changed oil not too long ago. Maybe oil cooler lines?

2005 with 215,000 miles

If you still have the plastic tube, chances are its cracked. Dont think it would leak enough to cause low oil though, unless your turbo is shot. Could be glow plug harness too. That would leak enough to lower the oil level, but you would tend to see it on the ground.