In 1967, Dom Antônio obtained permission to operate the Major Seminary, with Philosophy and Theology courses (later transferred to Campos).

[6] In 1968, the Catholic conservative group Tradition, Family and Property organized a campaign to collect signatures denouncing what were perceived as leftists in the Church.

Until his resignation on 29 August 1981, the Tridentine Mass continued to be celebrated throughout the Campos diocese, along with all the other traditional Catholic practices and devotions in Latin.

Having submitted his resignation as required upon turning 75, he was replaced as bishop with the appointment of Carlos Alberto Etchandy Gimeno Navarro [pt] to succeed him on 29 August 1981.

Communications from Pope John Paul II and curial officials, both before and after the ceremony, did not mention de Castro or note his role.

[9] One Vatican statement described him as a co-consecrator and excommunicated,[10] but others, including Pope John Paul's letter on the consecrations omitted his name.