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So, bad got worse..... The plan was to drill into it a bit and then use a screw extractor to pull out the bolt shaft. While I went to the store to buy the appropriate extractor, the guy I have been working with drilled into the bolt. When I returned, he had drilled into it, and had chewed up the threads on the top side of the hole (see pic), making it impossible to use an extractor (should've done it myself I guess).

So, now the situation is that there is a 9mm (as measured) hole drilled into the case, with part of the old bolt still stuck inside. While it may still be possible to get the old bolt out, I don't want to take any chances of getting metal into the motor by drilling through, so I think creating a new, shallower threaded hole may be the way to go here. I am thinking that I will probably go ahead and try to clean up the hole to remove the first 9mm of old bolt, then tap the next larger diameter of metric threads into that. This job is becoming a nightmare.