I dont believe Gadolim are infallible but I do believe that they have special siyatta dishmaya and certainly we had many Tzaddikim in the past who had Ruach Hakodesh, it was not so long ago that the Steipler zatzal was niftar, he was known to have open Ruach hakodesh there are many stories about him.
Heres the grasshopper story I got it from matzav dot com.
Approximately eight years ago, Rav Chaim was learning Maseches Chullin and a sugyah relating to chagovim, grasshoppers. Rav Chaim realized that he needed to see a grasshopper to better understand the Gemara – apparently he had never seen a live grasshopper before – and asked his daughter to bring him one. She tried, but reported to her father that she failed to find one. He went back to the sugyah, and lo and behold, a grasshopper came hopping through the window, landing on his Gemara. After examining it, he let it go. As he continued through the sugyah, he realized that he needed to study the hind legs a bit more, but the grasshopper was long gone. Before closing his Gemara, a second grasshopper hopped in and on to his Gemara, giving him the ability to study its hind leg in detail.