2004 Ford Falcon Bleeder screw/valve

First of all, wash all of that penetrating oil off with brakes parts cleaner. The slightest hint of petroleum product in brake fluid will contaminate the entire system. That is a real expensive repair. You can grab the bleeder screw with a vise grip pliers. Use a hammer to bang on the caliper right next to the bleeder screw. That will distort the casting and help break the bond in the threads. If you have an acetylene torch, heat the bleeder screw until it gets red hot, bang on the casting, then dribble a little water on the screw to quickly shrink it. Try to keep the water off the casting as much as possible. Don't try this with a propane torch. The flame is not nearly hot enough, and with a prolonged attempt to get it hot enough, the rubber square-cut seal inside can be damaged.

As a last resort, just unbolt the caliper, hold it with the hose connection at the highest point, and loosen the hose. The fluid will gravity-bleed through that connection. You may need to loosen the cap on the reservoir so no vacuum builds up in it. That will prevent the fluid from running down.

That's up to you. If you're going to replace the calipers at the next brake job, there's no sense in replacing the bleeder screw now, as long as you can get it loose and tighten it again with a vise grip pliers. Once you get it loose, you may be able to pound on a six-point socket to turn it. If you do choose to replace the screw, any auto parts store will have a replacement but you may need to take the old one along in case they need to match the threads.