A gross generalization. Lucio and Julio Cesar, anyone?
Yup, the generalization that all Brazillians turn bad is ridiculous.
Even when Ronaldo was massively overweight he still scored plenty of goals and even now he still holds around 0.6 goal pr game in the Brazilian league.
Carlos never turned bad, his form decay was a natural development due to his age.(if anything, carlos shows the opposite of decaying early)
Rivaldo was pretty bad after he joined milan, but he was already 30+ then.
Ronaldinho was the best playmaker in Serie A last season, he doesnt have his best days infront of him, but is still a great player.
Brazilians doesnt decay any earlier or more than other players, its a ridiculous myth started by morons. The brazilians stand out because in their absolute prime they are the best on the planet and then its more noticable when they just become "good players".