This rubberized roof patching
material takes advantage of a unique penetrating oil called Penetrex.
You can find it at most
stores for around 10 dollars a can.
It's sticky, and messy, and
sometimes requires multiple applications. I've got a dedicated pair of
gloves and spreading trowel that I wrap up in a bag and store in the
roof repair section of our office. It would take way too long to clean
all that gunk off the trowel.
I'd expect that "penetrex" stuff just to be some kind of solvent.
And indeed, looking at the MSDS of this roof repair gunk, that "penetrex" stuff is just Stoddard solvent, aka white spirit.
White spirit is widely used as a paint thinner and paintbrush cleaner. But these days water-based paints are replacing solvent-based paints since long term exposure (think professional painters) can damage the nerves, and it is a known carginogenic (see the MSDS, second page). Wear gloves that block it. Butyl rubber should work, I think. Leather probably doesn't.
Definitely use separate tools and gloves for this stuff.
So what you've got here is basically a heavy crude oil destillation leftover (asphalt), diluted with white spirit.