“Reb Sholom Wolpo wrote a book called Yechi Hamelech explaining how the Rebbe is/was bechezkas Moshiach. That Sefer got the haskamos of Reb Moshe and Rav Ovadia among others.”
Do your research. The haskamos were given only on a Halocho sefer written by Wolpo about Mashiach. They did not give haskomos on the sefer saying that the Lubavicher rebbe was/is bechezkas Mashiach. That came out a number of years after Reb Moshe was niftar!
Chabadpedia has the entire story.