What motor?
If those bolts came loose during operation, that would mean, its expect the worst, hope for the best. If they did not come loose while running, then how did they? Improper installation is a possibility. I guess, if the crank threads are buggered, you could possibly tap them to the next size up and find oversize bolts of the correct type. I would be leery of using thread replacement kits in that area. If the motor has a car application, the bolts should be similar.

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Chris
84 280sl
82 300d euro