If this code crashed all the time there'd be a business need to fix it and I could justify spending time on this.
But that's not what we're discussing here, we're discussing warnings that have been ignored in the past, and all of a sudden I'm supposed to take the political risk to fix them all somehow, even though there's no new crash, no new information.
I don't know how much freedom you have at your job; but I definitely can't just go to my manager and say: "I'm spending the next few weeks working on warnings nobody else cared about but that for some reason I care about".
What would you do if the code you inherited crashed all the time?
Come up with a strategy for fixing them steadily until they're gone.