I know it's a case of locking the stable door after the horse has bolted, but you're screwing those bolts into aluminium - they have a very low torque setting, barely more than "nipped up" really. I don't think those bolt holes go all the way through so using a longer bolt will only work if there's enough clearance for it. To fix it the RIGHT way you need to take the cover off completely, measure the wall thickness of the hole, and if there's enough clearance tap and fit a helicoil. That's a lot of work though, so go with airguy's suggestion of a 5mm longer bolt first - I think there's one in the the sprocket cover, so you could "try before you buy".
Matt
