; to a local dollar store and buy a bottle of "Awesome". It's cheap and always did the job for me when I had an aluminum sided trailer. Be aware, though, it will also take off any layer of polish you may have on the trailer. Once you get it clean and repolished I found a good coat of New Finish will clean it easily in the future.
buy a cleaner wax, if you are using a strong soap or chemical that is going to strip the wax or polish off anyway why not just use a cleaner wax and save a step. the cleaner wax will lift the black streak and also apply a thin protective coat.
You can layer another coat of wax over it if you like but not necessary.
It works great and you don't risklosing the shine altogether.
Thanks for all the suggestions. It's niceto know there's aplace to go when you need answers. Now I should be able to remove them darn black streaks that make my 2 year old trailer looklike it's a 10 year old trailer.