'03 Cadillac CTS transmission oil or power steering oil leak?

Every day there is a very small drop of a dark orange oily substance on my garage floor, but I can't tell if this is power steering fluid or transmission fluid. I can't tell be getting under my car. It is easy to check the power steering level, but the leak is so small that I don't notice the level decreasing if that is what it is. I also put Lucas Stop Leak in it, but still see the spot on my garage floor.

The transmission is sealed, so there is no way of checking the level. How do I tell if it is transmission fluid or power steering fluid that is leaking? The onboard computer is reading "transmission fluid 100%". Does that just tell you if the transmission fluid is dirty, or will it tell you if the level is low also?