Im Stumped by This Stain

Inspected this house today and the roof and gutters all looked good except for the staining at this one leader drain. Gutter had leaf guard attached so i couldn’t see inside. Any ideas what would cause this???

Could be a steel valley above feeding rusty water into the gutter or steel gutters or the leaf guards could be steel. .

My first thought is a hand full of nails or gutter clips left in the gutter and they are rusting?

No valley above, gutter and guards are aluminum. it would take a box of nails to make that much rust. I was looking back at my pictures and the attic A/C unit’s condensate dumps into that gutter - I’m guessing that’s the culprit.

Lol… We have a winner!!
By the way, I found a box of nails in a gutter a few months back( actually 12 sleeves for nail gun.) the gutter was overflowing . So in this business be surprised by nothing and consider everything…:slight_smile: