The news recently came out that Fr Vlasic, who had been a spiritual director at Medjugorge some years ago, was laicized. That's prompted a lot of commentary on Catholic blogs about the apparitions.
It's up to the Church to decide if the apparitions are authentic or not. I'm not calling them authentic or not authentic.
But the case of Fr Vlasic really has nothing to do with that question. He wasn't one of the seers, and his former relationship with them is irrelevant to the question about the apparitions.
History can give us some light here. Back in the mid 1800's, the Church approved the Marian apparition at LaSalette in France. Mary appeared to two children, a boy and a girl, Melanie and Maximin. In later life, both had various problems and difficulties and didn't turn out to be quite as saintly as say, St Bernadette. But that doesn't invalidate the apparitions they experienced.
All of this is a reminder that holiness doesn't consist in having visions. In fact, St John of the Cross was rather severe toward those who had any desire for visions. Instead, the way of faith is the way God leads us: "We walk by faith, not by sight." Visions fall into the category of charisms. These are spiritual graces that God sometimes grants not for the sanctification of the person receiving them, but for the spiritual good of the wider Church. In approved apparitions, Mary generally gives some message calling people to prayer, repentance and conversion of life. It's great if the seers live that message themselves. But if they don't, Mary's message remains just as valid.