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Personally I would be priming/undercoating the factory coating with a tinted primer/undercoat after cleaning/degreasing it and then using 2 coats of an exterior eggshell. Maybe overkill. If what you have is a single coat of eggshell over a factory primer I would be asking why it's been done that way.
Most exterior paints will 'guarantee' 8 years (for dark colours), that requires proper preparation. The details are normally printed on the label.
Cheers! Doubt it was primed with anything other than the standard primer a cast iron gutter comes with. He also painted an extra section that was pre-painted with a gloss of some sort as it’s the OG gutter.
It’s not big deal but the insurance co want me to sign a thing to say I’m happy etc - I’ll have zero come back after I sign it.