Answer:
My second is performed by my first, and it is thought a thief by the marks of my whole might be caught.
What can go up but never come down?
What never gets any wetter no matter how hard it rains?
What never asks questions but is often answered?
Though I should be unique, you've made most of us the same. I would be stronger, if my characters were stranger.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.