I gave up on EZ outs for this long ago due to what you have experienced. Exhaust bolts are harder than Chinese arithmetic after years of running at high temps. I try and get the broken bolt ground flat if possible....center punch (using a "Good" punch) and then a center drill. If I get any where near center it is just a patient process of going up one or two bit sizes at a time. When I get close I use a caping chisel and remove whats left while trying to save the threads. Not always successful.
Thanks for the offer on the burr tool.
Thanks for the offer on the burr tool.