I had similar happen in aluminum block push mower. I bumped up from 1/4 to 5/16" bolt.

I would use a helicoil and I would do it without removing and replace the chain cover.

10 N·m maths out to just shy of 2000# clamp force. The block just age/heat cycle weakened and couldn't handle the force anymore.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)