Here's an off-the-wall solution to ponder: fill the hole with a metalaized two part epoxy such as J-B Weld, allow it to fully cure (1-2 days) then drill and tap it. I've had good success with this product in other applications and the packaging says that it can be drilled and tapped. If it doesn't hold, you should be able remove the "insert" from your bolt with a wire brush and move on to a different solution.