Did you quarantine him for a month? I wasn't quite clear on that. Coming from a nasty place like that, especially, you'd want to have kept him away from your flock for that long for any respiratory symptoms to come to the surface in order to protect your hens.
We have only purchased one grown bird, my first rooster, a BR, in the entire going on 7 years of owning chickens. His environment was not nice, either--pen back in dark woods, full of mud, black tank of drinking water, only corn for nutrition, living with a grown turkey who decimated his comb.
Hawkeye was in quarantine for 5 full weeks in the house in a large wire dog crate, during which time we treated his bad lice infestation, his case of favus (fungal infection of comb/wattles/face), wormed him and made sure he was not a carrier of some respiratory illness before allowing him access to the hens. And this kid who owned him was an FFA kid, if you can believe it! Hawkeye paid us back in spades by being a true gentleman in every sense of the word, but it was stressful always wondering if he'd bring some disease with him so we have never bought started birds since that time, only hatched them here from reputable breeders who never treat respiratory gunk (they take an axe to symptomatic birds).
Hope your rooster is as wonderful as Hawkeye was.