If what you say was true--what was he doing as an "expert" at the Council?
Fr. Schillebeeckx became radicalized after the Council. To give one example, in 1963 he stated of the teaching against contraception: "It is unthinkable that in such an important question of daily life the Church could err in its solemn teaching". But in 1968 he rejected Humanae Vitae.
One can become more radicalized as time passes. Mr. Drolesky is an example of that. Cardinal Ratzinger is an example of one who became less radicalized. He was one of the experts advising one of the most liberal prelates at the council and in subsequent years backed away from those views.