My donuts also were shot after 6,000 miles. 2 of 3 were completely gone and only a remnant of the last one was still there. My buddy had the same problem on his Apex, except he has 4 to deal with!
To remove those stubborn clamp bolts and header mounting bolts, use a propane torch to heat them up cherry red and then try. They come out very easy once you apply some heat.