Snapped EXUP valve bolts off flush with header. Can't drill bolts out to re-tap.

Recently I heard a rattle in my exhaust, so I decided to investigate by removing the exup valve and seeing what was in there. After doing some research later I found out that some FZ's after awhile will develop a rattle from the small bushing/washer located on the exup valve. Well through the process of removing the cover, I snapped two bolts holding the cover on flush with the exhaust. I used very little torque and they just decided to snap (again, heard this was common.) I thought well, drilling these out shouldn't be an issue, boy was I wrong. I can only drill out maybe a quarter of an inch and now I cant go any farther. I've gone through 4 bits to see if they were the problem and even tried a Dewalt Cobalt bit and still can't drill through that bad boy. If I could just get it a little farther to tap I would be good, but I've ran into a brick wall it seems like. Does anyone have any ideas how I can drill any farther into this bolt so I can get a heli-coil or something in there? I've completely ran out of ideas and patience.
 
Since you have already drilled them it may be too late but I have welded nuts (or washers) to broken off bolts and let it cool. This works often. Sometimes I weld a bigger nut to the first one just to add heat.
 
What size drill bit you using ? ,, start with a 1.5 mm or similar and work your way up in small increments , time consuming but the only way :)
 
I started out with a small bit and slow speed, really seemed to get the job done. I got the drilling far enough and wide enough to insert a heli-coil. Tomorrow I'm going to clean out the crevice with a q-tip and apply a thin layer of JB Weld in there for the heli-coil to be inserted. Wish me luck!
 
I just replaced my whole header with a fleabay Unit for $60. Machinist wanted $100 to drill and tap the broken bits and I've done it before with poor results. Took 20 minutes to swap the header - simplicity and lack of hassle were worth it.

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The same thing happened to me eight years ago. I took the header of and took it to my local Yamaha dealer. The dealer was able to remove the broken bolts and charged very little....can’t remember, maybe $30.
 
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