Bolt Question

On my way to work this morning the damper lower bolt snapped, so instead of doing my proper work I decided to fix it, having use of welders grinders etc, anyway I managed to free the broken bits and the only bolts we have available are cap screws rated at 12.9 so Iv'e fitted one of those to get me home, will this grade of bolt be ok for long term use? or do I need to get the proper 10.9 flange bolts?

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