Center punch the bolt, drill a hole, starting with an 1/8 drill stepping up to about a 9/32. This will allow the threads to collapse enough to loosen it up and remove it. Your easy out should stay up high enough not to force out the threads still inside the mount. Next, go ahead and drill completely through the mount, a 21/64. You will have to flat bottom countersink it on the bottom about 1/4" and use Allen Head cap screws (to clear the levers) to go up from the bottom. Doing this will eliminate the mirror adapters and allow you to use ANY mirror you choose. I did this to mine, not due to stripping it out, but to eliminate those ugly adapters. If you use a 21/64 drill, it will accommodate a 8MM or 5/16 bolt, whichever mirror you choose. Here is how the mirrors look doing it this way. It's a bit tedious but not difficult.
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