Do I need to replace the header bolts when I install this gasket?

Not necessarily. If your existing bolts are in good condition and torque down evenly, you can reuse them. Check them for corrosion or cross-threading first—if they're questionable, new header bolts are cheap insurance against leaks.

Can I reuse the old header bolts and just swap the gasket?

Yes. Clean the bolts and the header flange thoroughly before reinstalling. Any carbon buildup or debris between the gasket and flange will cause a leak, so take time with the prep work.

What if exhaust is still leaking after I install this gasket?

Strip the bolts and flange again, verify the flange surface is flat and clean, and reinstall with even torque. If leaking persists, the header flange itself may be warped—check that with a straightedge before blaming the gasket.