Originally Posted by MCallahan

If it's a stripped bolt hole, you'll have to helicoil it to fix it right. Another possibility is that the wrong bolt has been installed during a replacement, was too short by a little bit, only engaged a few threads, and pulled those out when tightened. That's easy to check by removing the bolt, sticking a length of wire into the hole to measure depth of the hole, then comparing to bolt length. General rule is 1 1/2-2 times bolt diameter for thread engagement. An 8mm bolt should have 12-16mm (1/2" to 5/8", roughly) of thread engaged. If the bolt was 4mm short, it could easily pull the first few threads out when torqued to spec, or just under "feels right" tightening.