Having seen the latest pics posted. I can see what the black mark is. I work with this product everyday. What is happening is when they assemble these panels together, they apply a silicone caulk bead in the joint. Well, silicone has an oil base, and over time and weather, the oil from the silicone runs over the panels. since it is a strick clear oil, it collects dirt in the air causing it to streak. I am sure they clean it from time to time, but it will continue to come back. That is what is going on with the black marks.
Just a side note, the company that installed the alucobond panels on SSE, went out of business due to this complex project!
Later days!
AJ