The man's evidence at court was consistent and compelling. He had a clear memory of what had happened, despite the decades, and was able to recall details from the room, the door and even the door handle.
Manukau District Court
Crown prosecutor Jasper Rhodes said Gibbs took care in choosing the places where he would abuse the boy - including his locked office and even the attic space above his office.
Mr Rhodes acknowledged the complaint had only been made relatively recently, because the man - out of concern for his parents - had waited until they had passed away before approaching the police.
Gibbs denied the offending took place. His lawyer argued the complainant made up the abuse in an effort to explain his homosexuality before the law was reformed in the 1980s.
Gibbs, who has previous convictions, will be sentenced in February.