Randy,
Contact a local power washing supplie store in you area. Ask them what they think is the best chemical for cleaning painted aluminum.
We have a chemical in our area, can't remember the name. But I will look it up for you.
This chemical is great. It is a spray on and rinse of product. Now and then you have to scrub a little. The gutters come out like new.
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Dan Flynn
Flynn Service Pro
www.powerwash.net
708 715-4205