Broke my water pump bolt. Now what? (Update - broken bolt is out)

After all your penetrant soak...suggest you clean the protruding stud and a matching nut with solvent. Use red loctite in the nut and tighten that thing up. Let it cure. I never tried this but red loctite is the mother of all thread lockers in my experience. My guess is it will turn the broken bolt out. If it fails, no harm to any other method you may want to try.