I know three “Fr Brian’s.” I guarantee you there’s probably about seventy to each episcopal province. I even knew a “Fr Brian O’Brien” but he’s long gone, rest him and bless him.
OP, if I were you, I’d get a copy of the GIRM and give it to him and say “look, Father, this is what you signed up for. This is what you’re to do. You’re a Catholic priest and this isn’t cut and paste. Either you obey the commandments of the respectful offering for liturgy, or you don’t.” See what he says. If he doesn’t, take it to the bank…the bishop.
There’s a priest in our diocese who is prone to doing this. He doesn’t mention the pope or the bishop in the Eucharistic prayer, he omits parts of the Mass such as the penitential rite, the post-Communion prayers, the collect even, sometimes, if he finds the “wording is inappropriate.” Wouldn’t know but he was St Jerome reincarnate.
But at the end of the day, these men are consecrated men. They deserve our respect, and our prayer, but even a gentle correction sometimes doesn’t go amiss as long as we understand that we are below them, in our theological knowledge and position of power. Many lay saints have been known to have corrected their priests.