The reason you see so many different answers is that the chemical make-up of the streak varies considerably. Part of it is probably chalk (for RVs with a rubber roof), but the rest is dirt and grime from the air and rain water that has accumulated on the roof and then runs down. In some areas that means acids (acid rain content), smoke stack residue, tree saps, greases, bird dung with various berry and nut juices or insect residue, etc. And the degree to which is penetrates the finish on the RV depends on the material, paint vs fiberglass or aluminum, gel coat, clear coat or none, etc. You may find something that works great on your rig but has little effect on somebody else's. Or the streak content may change if you camp in a different region.