At the top of the struts are rubber strut mounts. These isolate the top of the suspension (shock) from the body. They decay after a while (most likely the black soot you are seeing)
This site sells them:
Strut Mounts at a pretty good price.
The sound could also be coming from bad front lower ball joints. Often rust dust is evident around the intersection of the strut and lower A-arm (ball joint) and broken rubber dust boot.
It is best to change all of the shocks at once for an even pleasing ride. Next best are pairs (the fronts or the rears). You can of course change just one strut but you will most likely noticed the difference if the unchanged strut is old.
Keep us posted,
Haas