If it's alum, just wash it with TSP (Tri Sodium Phosphate). Rinse with plenty of water all the way down the sides. Right after the top we always washed the sides with a Turtle Wax Wash. After it's dry go up and remove any cracked caulking with a plastic scraper. Then just use the self leveling sealant around every opening through the alum, vents, skylights, AC etc.
I had a TT with alum roof, loved it. After 18 yrs still looked new except for some hail indentations. We never had any black streaks using the TSP. Just make sure to rinse the sides or it will fade the paint. I used a cup of TSP powder in about 3 to 4 gal of water.