Looks like a pretty big chunk missing, do you have the piece that broke off?
Hard to tell from the angle of that photo, but if that hole isn't part of an oil passage, then maybe you could tap it out, and bolt in a piece of square stock?
I don't have the piece, and there weren't any stray pieces of metal in the crankcase when I took it apart. The hole doesn't appear to be part of the oil system, and has some worn threads. I think that maybe someone at some point may have tried to bolt something in there to fix the problem as you suggest.
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