Mystery fluid found under car, dealership can't find leak...

I took my '17 Prius Prime Advanced in for its 15K service this morning. When I got home, since it wasn't parked in the garage, I saw a bunch of tiny "puddles" (dime-sized) under where the front passenger side of my engine always is. They were black and viscous (about like hand soap, and somewhat hard to wash off my fingers), but not slippery. When I mopped them up, they are green and black on a white paper towel (photos attached).

I called the dealership and asked them to check. They said they can't find any leaks, and that the fluid is only on the underbody and some pooled up in the splash cover. They say that it must be something I drove through and picked up. They say the coolant is pink, tranny fluid red, oil golden and the brake fluid is clear/golden. So they don't think it's from my car.

Any opinions here as to what this fluid might be, and where it might have come from?

 

Thanks. Yes, and that is the plan for now. Still wondering what the fluid might be. Must've come from another car if not mine.

 

I sure don't remember driving through anything, and it's San Diego. I can't remember the last time I drove in the rain. Also, it was very thick, not watered down at all. It was about the consistency of pancake syrup.

 

I should've mentioned that it had no smell whatsoever. It was also not thick enough to be grease. Every tiny "puddle" of it was the same consistency. It was like pancake syrup.

 

They did mention grease, but they said the boots were intact and there was no sign of it coming from anywhere. Also, I don't think it's the right thickness for grease. It's too much of a liquid. It's like pancake syrup. Grease, in my experience, is more along the lines of toothpaste.

 

I'm presuming that's a joke.

 

It was not very slippery, but it was viscous. It was not easy to wash off.