Runoff from equipment or adjacent materials can create localized conditions different from general atmospheric exposure. A coastal address alone may not explain a concentrated stain or corrosion pattern. The source should be investigated.
What to do next
Map the affected area and identify nearby equipment, drains, and materials. Coordinate the relevant trades when needed. A repair should address the local cause and compatibility rather than relying only on a coating or cleaning treatment over the visible symptom.
Related Perkins guidance
Contact Perkins Roofing to discuss your roof and the appropriate next step.