[ngoma]

Situation not particular to D24. No reason to cause you to abandon your project.

1. Soak it with penetrant, try a left-hand drill bit. Sometimes the drill bit working in reverse will unscrew the stud remains.

2. Weld a nut to the remains of the stud and unscrew it with a wrench. Hundreds of examples of this on youtube.

3. (requires the most skill) Drill the stud exactly perpendicular and straight into the exact center in increasing sizes drill bits until you can scrape out the last remaining bits of thread left from the threads in the head. Almost impossible to get the drill straight and centered. If you damage the threads in the head, you can drill oversize and use a Time-sert or helicoil.

4. (not recommended) EZout or similar. Often these break off in the stud leaving you worse off than before.


#2 is probably your best bet, telling you now.

Good on you for using the proper (special Volvo) exhaust manifold heat/tension washers, cleaning the threads, and using anti-seize.