Found this and it seems very strange given all the circumstances.
2002 model home in a development. In the electrical panel every single branch wire ,neutral, ground, main conductors are black. Only thing that is not black is one new branch installed and obvious it’s not original. Pulled outlets and switches in every room and all are clean. Fixtures are clean.
No corrosion inside air handler. The outlets in garage are clean and no discoloration on top of water heater. Drywall in attic says Palatka, Fl
Exterior has been repainted. So narrowing it down to maybe the irrigation has high sulfur and gotten into the panel? It is on an exterior garage wall.
Garage door faces North so if maybe open during watering ? Just looking for input. Buyers are real leary.