take a slow deep breath...then spray the heck out of the busted bleeder screw. take a drill bit and drill the center just to rough it up from the spray and it will also generate some heat, then put an easy out into it and twist it out. moving forward, that caliper is on the all of the later cb750 K and 75-76 F models...find one on ebay that looks better than yours. clean it, bead blast it, put in a new seal, clean up the best of the two pistons you now have , etc and you will have fine brakes for a long time.....