Can you find me the video with that story involving the Maharsha and Kings David and Shaul?

Yes, I can help you with that. The story you're looking for is an incredible account involving the Maharsha, who was known in his town simply as Shmuel the shamash. The people mocked him and threw mud at him, not knowing he was actually the Gadol HaDor, the greatest Torah scholar of the generation. In Shamayim, there was a machloket, a dispute, between David HaMelech and Shaul HaMelech that they couldn't resolve. They decreed in Heaven that only the Maharsha could give them the final answer. So for several nights, David HaMelech and Shaul HaMelech came back to this world and appeared to the shamash of the shul, asking where the Maharsha was. The shamash didn't realize that the Maharsha was the very person everyone was mocking. Eventually, Eliyahu HaNavi himself appeared and revealed the truth to the shamash - that these beautiful, holy visitors were coming to learn with the Maharsha, and that Shmuel was actually the great Maharsha HaKadosh. The shamash was warned that if he told anyone what he saw, he would die. But he understood his obligation was to reveal the truth so that the community would stop disgracing this tremendous tzaddik. He called a town meeting, told them everything, and immediately after finishing his testimony, he died on the spot. The full story with all the details can be found in the video titled "MUSSAR Pirkei Avot (155) The Real Jewish Kings 6" on the BeEzrat HaShem website.