That's very interesting. (And also slightly hilarious -- if I had to choose between motor oil and TP, which would it be? Both are the basis of civilization as we know it. Hmm.)

I know the base petroleum is completely recyclable. They clean out the crud, put in new additives, and sell it to you again.

It's the additives I'd worry about. Though in a real pinch, TP filtration plus a little fresh oil might keep an old Toyota or Chevy rolling a bit longer.