I’d also recommend the documentary. Needless to say (or it ought to be needless) the status of Fr. Gruner has no bearing on the arguments made in the documentary. They can, and have been, made by others. Most notably the mainstream Italian Catholic journalist Antonio Socci.
Antonio Socci’s stuff doesn’t read like journalism. it honest to God reads like some weird cross between the supermarket tabloids and conspiracy you find on the internet. That doesn’t mean it isn’t true, but it’s a mark against it - a reason to be skeptical. If his material were indeed true, I wouldn’t think he’d need to use the style of writing that he does.
And this is really part of the broader aspect of discernment when dealing with Fr. Gruner’s stuff. You’re correct that his personal disobedience, obedience, being a nice guy, being a nasty guy, or whatever doesn’t mean that what he says is or is not true. However, we’re dealing with spiritual matters, being presented from a priest - a hopefully spiritual guy.
When we look at the lives of all the saints, they weer
never disobedient, no matter what the truth was. When their superior, bishop, or other ecclesiastical authority told them to stop speaking about the apparition they saw, or the groundbreaking theology they had developed, they did. They humbly submitted to their superiors, and God brought the validation of their cause about by His own power.
When you look at Fr. Gruner, he is in the same position. He has a message he believes he must reach the people with. However, he has been manifestly
disobedient about it. He has accused John Paul II, then Cardinal Ratzinger, Cardinal Bertone and others of lying. He has tried to
break into a cloister to speak with sister Lucia. One of his former assistant who no longer subscribes to his theories after meeting with Sister Lucia has been refused to be paid until he retracts his report of what she told him.
None of this means in a concrete sense that what Fr. Gruner is saying is untrue. However, every rule of spiritual discernment in the books says that we ought to hold Fr. Gruner’s teachings with
extreme skepticism. That’s the key. This is a spiritual matter. If Fr. Gruner is correct, he is correct by Grace, but if he were so enlightened by Grace, would he behave as he does? The saints and the traditions of spiritual discerrnment tell us that he would not.
What it comes down to is two sides. On the one side, Fr. Gruner and other disobedient people (e.g., Diamon brothers) claim the third secret remains hidden and present good evidence and hard to answer questions. On the other side, men of manifestly impeccable character such as John Paul II and Benedict XVI assert that the third secret is revealed, backed up by good evidence and hard to answer questions.
On the level of evidence and facts, two experts on the subject could go back and forth all day in argument. What it really then comes down to is, would Pope John Paul II lie to the universal Church? Did Cardinal Ratzinger lie? Those are the only question one needs to consider to see the truth of the situation.
Peace and God bless