A guy at the Daytona swap meet showed me his trick for freeing rusted bleeders and I have used it 40 times since
He warmed the caliper with a heat gun for about 90 seconds and hit it with a 50/50 mix of ATF and acetone, and that bleeder walked right out. I had been snapping these things off for 12 years before that, so what is your go to for a bleeder that is already rounded off?